Номер 790, страница 191 - гдз по геометрии 10-11 класс учебник Атанасян, Бутузов

Геометрия, 10-11 класс Учебник, авторы: Атанасян Левон Сергеевич, Бутузов Валентин Фёдорович, Кадомцев Сергей Борисович, Позняк Эдуард Генрихович, Киселёва Людмила Сергеевна, издательство Просвещение, Москва, 2019, коричневого цвета

Авторы: Атанасян Л. С., Бутузов В. Ф., Кадомцев С. Б., Позняк Э. Г., Киселёва Л. С.

Тип: Учебник

Издательство: Просвещение

Год издания: 2019 - 2026

Уровень обучения: базовый и углублённый

Цвет обложки: коричневый с ромбами

ISBN: 978-5-09-103606-0 (2023)

Допущено Министерством просвещения Российской Федерации

Математика: алгебра и начала математического анализа, геометрия

Глава 7. Метод координат в пространстве. Движения. Параграф 3. Движения, дополнительные задачи - номер 790, страница 191.

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                      ]
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                    }
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                        0 => App\Models\Term {#1065
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                    }
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                    }
                    "field_level_of_education" => Illuminate\Database\Eloquent\Collection {#1072
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                        0 => App\Models\Term {#1073
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                      ]
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                        0 => App\Models\Term {#1075
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                            "field_cases" => array:6 [ …6]
                            "field_color" => null
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                        0 => App\Models\Term {#1077
                          #connection: "mysql"
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                            "created_at" => "2026-04-10 13:58:26"
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                      ]
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                    "field_under_the_edition" => Illuminate\Database\Eloquent\Collection {#1078
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                    "field_link_to_source" => null
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                      ]
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                    }
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                    }
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                    }
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                    "field_cover_color" => Illuminate\Database\Eloquent\Collection {#1082
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                        0 => App\Models\Term {#1083
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                            "created_at" => "2026-04-10 13:58:26"
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                            "name" => "коричневый"
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                          ]
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              ]
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            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1084
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            }
          ]
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            "field_branch_order" => "7"
            "field_url" => null
            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1050}
            "field_page_start" => "160"
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            "field_display_task_interval" => "0"
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            "field_branch_title_in_content" => "0"
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            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1086}
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          ]
        }
      ]
      #escapeWhenCastingToString: false
    }
    "parent_branches" => Illuminate\Database\Eloquent\Collection {#1121
      #items: array:2 [
        0 => App\Models\Branch {#1129
          #connection: "mysql"
          #table: "branches"
          #primaryKey: "id"
          #keyType: "int"
          +incrementing: true
          #with: []
          #withCount: []
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          #perPage: 15
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          #attributes: array:24 [
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            "created_at" => "2026-04-10 13:58:26"
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            "field_display_title" => "Метод координат в пространстве. Движения"
            "field_branch_order" => "7"
            "field_url" => null
            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1130
              #items: array:1 [
                0 => App\Models\Term {#1047}
              ]
              #escapeWhenCastingToString: false
            }
            "field_page_start" => "160"
            "field_branch_display" => "0"
            "field_branch_expanded" => "0"
            "field_display_branch_in_title" => "1"
            "field_display_task_interval" => "0"
            "field_display_branch_page" => "1"
            "field_branch_title_in_content" => "0"
            "field_navigation_title" => null
            "field_metatags_title" => null
            "field_metatags_description" => null
            "field_h1" => null
            "field_description_top" => null
            "field_description_bottom" => null
            "field_branch_cover" => []
            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1131
              #items: array:1 [
                0 => App\Models\Book {#1049}
              ]
              #escapeWhenCastingToString: false
            }
            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1132
              #items: []
              #escapeWhenCastingToString: false
            }
          ]
          #original: array:24 [
            "id" => 744405
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "field_display_title" => "Метод координат в пространстве. Движения"
            "field_branch_order" => "7"
            "field_url" => null
            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1130}
            "field_page_start" => "160"
            "field_branch_display" => "0"
            "field_branch_expanded" => "0"
            "field_display_branch_in_title" => "1"
            "field_display_task_interval" => "0"
            "field_display_branch_page" => "1"
            "field_branch_title_in_content" => "0"
            "field_navigation_title" => null
            "field_metatags_title" => null
            "field_metatags_description" => null
            "field_h1" => null
            "field_description_top" => null
            "field_description_bottom" => null
            "field_branch_cover" => []
            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1131}
            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1132}
          ]
          #changes: []
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          #classCastCache: []
          #attributeCastCache: []
          #dateFormat: null
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          #touches: []
          +timestamps: true
          +usesUniqueIds: false
          #hidden: []
          #visible: []
          #fillable: []
          #guarded: array:1 [
            0 => "*"
          ]
        }
        1 => App\Models\Branch {#1133
          #connection: "mysql"
          #table: "branches"
          #primaryKey: "id"
          #keyType: "int"
          +incrementing: true
          #with: []
          #withCount: []
          +preventsLazyLoading: false
          #perPage: 15
          +exists: true
          +wasRecentlyCreated: false
          #escapeWhenCastingToString: false
          #attributes: array:24 [
            "id" => 744410
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "field_display_title" => "Движения, дополнительные задачи"
            "field_branch_order" => "3"
            "field_url" => null
            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1137
              #items: array:1 [
                0 => App\Models\Term {#1134
                  #connection: "mysql"
                  #table: "terms"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
                  #withCount: []
                  +preventsLazyLoading: false
                  #perPage: 15
                  +exists: true
                  +wasRecentlyCreated: false
                  #escapeWhenCastingToString: false
                  #attributes: array:7 [
                    "id" => 32
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "Параграф"
                    "field_cases" => array:6 [ …6]
                    "field_page_check_not_needed" => null
                    "field_short_name" => "§"
                  ]
                  #original: array:7 [
                    "id" => 32
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "Параграф"
                    "field_cases" => array:6 [ …6]
                    "field_page_check_not_needed" => null
                    "field_short_name" => "§"
                  ]
                  #changes: []
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                  #attributeCastCache: []
                  #dateFormat: null
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                  #dispatchesEvents: []
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                  +timestamps: true
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                  #hidden: []
                  #visible: []
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                    0 => "*"
                  ]
                }
              ]
              #escapeWhenCastingToString: false
            }
            "field_page_start" => "187"
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            "field_navigation_title" => null
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            "field_metatags_description" => null
            "field_h1" => null
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            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1136
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              #escapeWhenCastingToString: false
            }
            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1135
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                0 => App\Models\Branch {#1045}
              ]
              #escapeWhenCastingToString: false
            }
          ]
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            "id" => 744410
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "field_display_title" => "Движения, дополнительные задачи"
            "field_branch_order" => "3"
            "field_url" => null
            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1137}
            "field_page_start" => "187"
            "field_branch_display" => "0"
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            "field_display_branch_in_title" => "1"
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            "field_display_branch_page" => "1"
            "field_branch_title_in_content" => "0"
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            "field_metatags_description" => null
            "field_h1" => null
            "field_description_top" => null
            "field_description_bottom" => null
            "field_branch_cover" => []
            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1136}
            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1135}
          ]
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          +timestamps: true
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            0 => "*"
          ]
        }
      ]
      #escapeWhenCastingToString: false
    }
    "content" => Illuminate\Database\Eloquent\Collection {#1118
      #items: array:3 [
        0 => App\Models\Element {#1110
          #connection: "mysql"
          #table: "elements"
          #primaryKey: "id"
          #keyType: "int"
          +incrementing: true
          #with: []
          #withCount: []
          +preventsLazyLoading: false
          #perPage: 15
          +exists: true
          +wasRecentlyCreated: false
          #escapeWhenCastingToString: false
          #attributes: array:7 [
            "id" => 939935
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "edition" => Illuminate\Database\Eloquent\Collection {#1103
              #items: array:1 [
                0 => App\Models\Edition {#1111
                  #connection: "mysql"
                  #table: "editions"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
                  #withCount: []
                  +preventsLazyLoading: false
                  #perPage: 15
                  +exists: true
                  +wasRecentlyCreated: false
                  #escapeWhenCastingToString: false
                  #attributes: array:21 [
                    "id" => 2315
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "title" => "Условие"
                    "field_order" => "1"
                    "field_publisher" => Illuminate\Database\Eloquent\Collection {#1109 …2}
                    "field_content_type" => "free"
                    "field_content_mode" => "text, image"
                    "field_page_content_mode" => "image"
                    "field_content_text_checked" => null
                    "field_page_content_text_checked" => "0"
                    "field_solution_author" => "Автор"
                    "field_moderator" => "pasha"
                    "field_edition_type" => "statement"
                    "field_root_dir" => "0-"
                    "field_responsible" => Illuminate\Database\Eloquent\Collection {#1106 …2}
                    "field_comment" => null
                    "field_similar_book" => Illuminate\Database\Eloquent\Collection {#1107 …2}
                    "field_process_formula" => "wiris"
                    "field_edition_group" => Illuminate\Database\Eloquent\Collection {#1105 …2}
                    "field_content_source" => null
                  ]
                  #original: array:21 [
                    "id" => 2315
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "title" => "Условие"
                    "field_order" => "1"
                    "field_publisher" => Illuminate\Database\Eloquent\Collection {#1109 …2}
                    "field_content_type" => "free"
                    "field_content_mode" => "text, image"
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                    "field_page_content_text_checked" => "0"
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                    "field_similar_book" => Illuminate\Database\Eloquent\Collection {#1107 …2}
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                    "field_edition_group" => Illuminate\Database\Eloquent\Collection {#1105 …2}
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                  ]
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                    0 => "*"
                  ]
                }
              ]
              #escapeWhenCastingToString: false
            }
            "task" => array:2 [
              "refs" => "745205"
              "type" => "task"
            ]
            "text" => "<p> <b>790.</b> Основание ABC тетраэдра ОABC прозрачное, а все остальные грани зеркальные. Все плоские углы при вершине О прямые. Докажите, что луч света, вошедший в тетраэдр через основание ABC под произвольным углом к нему, отразившись от граней, выйдет в противоположном направлении по отношению к входящему лучу. (На этом свойстве основано устройство уголкового отражателя, который, в частности, был запущен на Луну для измерения расстояния до неё с помощью лазера.) </p>"
            "img" => array:1 [
              0 => array:5 [
                "name" => "790-1.jpg"
                "alt" => null
                "width" => "1559"
                "height" => 430
                "path" => "/media/geometrija_10/atanasjan-u23/0-00/790-1.webp?ts=1739436900"
              ]
            ]
          ]
          #original: array:7 [
            "id" => 939935
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "edition" => Illuminate\Database\Eloquent\Collection {#1103}
            "task" => array:2 [
              "refs" => "745205"
              "type" => "task"
            ]
            "text" => "<p> <b>790.</b> Основание ABC тетраэдра ОABC прозрачное, а все остальные грани зеркальные. Все плоские углы при вершине О прямые. Докажите, что луч света, вошедший в тетраэдр через основание ABC под произвольным углом к нему, отразившись от граней, выйдет в противоположном направлении по отношению к входящему лучу. (На этом свойстве основано устройство уголкового отражателя, который, в частности, был запущен на Луну для измерения расстояния до неё с помощью лазера.) </p>"
            "img" => array:1 [
              0 => array:5 [
                "name" => "790-1.jpg"
                "alt" => null
                "width" => "1559"
                "height" => 430
                "path" => "/media/geometrija_10/atanasjan-u23/0-00/790-1.webp?ts=1739436900"
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          ]
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            0 => "*"
          ]
        }
        1 => App\Models\Element {#1104
          #connection: "mysql"
          #table: "elements"
          #primaryKey: "id"
          #keyType: "int"
          +incrementing: true
          #with: []
          #withCount: []
          +preventsLazyLoading: false
          #perPage: 15
          +exists: true
          +wasRecentlyCreated: false
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          #attributes: array:6 [
            "id" => 942751
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "edition" => Illuminate\Database\Eloquent\Collection {#1095
              #items: array:1 [
                0 => App\Models\Edition {#1102
                  #connection: "mysql"
                  #table: "editions"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
                  #withCount: []
                  +preventsLazyLoading: false
                  #perPage: 15
                  +exists: true
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                  #escapeWhenCastingToString: false
                  #attributes: array:21 [
                    "id" => 2317
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "title" => "Решение 2"
                    "field_order" => "3"
                    "field_publisher" => Illuminate\Database\Eloquent\Collection {#1101 …2}
                    "field_content_type" => "free"
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                    "field_page_content_text_checked" => "0"
                    "field_solution_author" => "Неизвестный"
                    "field_moderator" => "pasha"
                    "field_edition_type" => "solution"
                    "field_root_dir" => "2-"
                    "field_responsible" => Illuminate\Database\Eloquent\Collection {#1098 …2}
                    "field_comment" => null
                    "field_similar_book" => Illuminate\Database\Eloquent\Collection {#1099 …2}
                    "field_process_formula" => ""
                    "field_edition_group" => Illuminate\Database\Eloquent\Collection {#1097 …2}
                    "field_content_source" => null
                  ]
                  #original: array:21 [
                    "id" => 2317
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "title" => "Решение 2"
                    "field_order" => "3"
                    "field_publisher" => Illuminate\Database\Eloquent\Collection {#1101 …2}
                    "field_content_type" => "free"
                    "field_content_mode" => "image"
                    "field_page_content_mode" => ""
                    "field_content_text_checked" => "0"
                    "field_page_content_text_checked" => "0"
                    "field_solution_author" => "Неизвестный"
                    "field_moderator" => "pasha"
                    "field_edition_type" => "solution"
                    "field_root_dir" => "2-"
                    "field_responsible" => Illuminate\Database\Eloquent\Collection {#1098 …2}
                    "field_comment" => null
                    "field_similar_book" => Illuminate\Database\Eloquent\Collection {#1099 …2}
                    "field_process_formula" => ""
                    "field_edition_group" => Illuminate\Database\Eloquent\Collection {#1097 …2}
                    "field_content_source" => null
                  ]
                  #changes: []
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                  +timestamps: true
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                  #hidden: []
                  #visible: []
                  #fillable: []
                  #guarded: array:1 [
                    0 => "*"
                  ]
                }
              ]
              #escapeWhenCastingToString: false
            }
            "task" => array:2 [
              "refs" => "745205"
              "type" => "task"
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            "img" => array:1 [
              0 => array:5 [
                "name" => "790-1.png"
                "alt" => null
                "width" => "694"
                "height" => 2717
                "path" => "/media/geometrija_10/atanasjan-u23/2-00/790-1.webp?ts=1739441698"
              ]
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          ]
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            "id" => 942751
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "edition" => Illuminate\Database\Eloquent\Collection {#1095}
            "task" => array:2 [
              "refs" => "745205"
              "type" => "task"
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              0 => array:5 [
                "name" => "790-1.png"
                "alt" => null
                "width" => "694"
                "height" => 2717
                "path" => "/media/geometrija_10/atanasjan-u23/2-00/790-1.webp?ts=1739441698"
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          #hidden: []
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            0 => "*"
          ]
        }
        2 => App\Models\Element {#1091
          #connection: "mysql"
          #table: "elements"
          #primaryKey: "id"
          #keyType: "int"
          +incrementing: true
          #with: []
          #withCount: []
          +preventsLazyLoading: false
          #perPage: 15
          +exists: true
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          #attributes: array:6 [
            "id" => 1352518
            "created_at" => "2026-04-10 13:58:26"
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            "edition" => Illuminate\Database\Eloquent\Collection {#1087
              #items: array:1 [
                0 => App\Models\Edition {#1096
                  #connection: "mysql"
                  #table: "editions"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
                  #withCount: []
                  +preventsLazyLoading: false
                  #perPage: 15
                  +exists: true
                  +wasRecentlyCreated: false
                  #escapeWhenCastingToString: false
                  #attributes: array:21 [
                    "id" => 5120
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "title" => "Решение 6"
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                    "field_publisher" => Illuminate\Database\Eloquent\Collection {#1093 …2}
                    "field_content_type" => "free"
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                    "field_page_content_text_checked" => "0"
                    "field_solution_author" => "Gemini 2.5 Pro"
                    "field_moderator" => "vadim"
                    "field_edition_type" => "solution"
                    "field_root_dir" => "6-"
                    "field_responsible" => Illuminate\Database\Eloquent\Collection {#1092 …2}
                    "field_comment" => null
                    "field_similar_book" => Illuminate\Database\Eloquent\Collection {#1089 …2}
                    "field_process_formula" => "katex"
                    "field_edition_group" => Illuminate\Database\Eloquent\Collection {#1090 …2}
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                  ]
                  #original: array:21 [
                    "id" => 5120
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "title" => "Решение 6"
                    "field_order" => "7"
                    "field_publisher" => Illuminate\Database\Eloquent\Collection {#1093 …2}
                    "field_content_type" => "free"
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                    "field_comment" => null
                    "field_similar_book" => Illuminate\Database\Eloquent\Collection {#1089 …2}
                    "field_process_formula" => "katex"
                    "field_edition_group" => Illuminate\Database\Eloquent\Collection {#1090 …2}
                    "field_content_source" => null
                  ]
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                  +timestamps: true
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                  #visible: []
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                    0 => "*"
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                }
              ]
              #escapeWhenCastingToString: false
            }
            "task" => array:2 [
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            "text" => "<p>Для доказательства воспользуемся координатным методом. Разместим тетраэдр $OABC$ в трехмерной прямоугольной системе координат. Поскольку все плоские углы при вершине $O$ прямые, мы можем совместить вершину $O$ с началом координат $(0, 0, 0)$, а ребра $OA$, $OB$ и $OC$ направить вдоль осей $Ox$, $Oy$ и $Oz$ соответственно.</p><p>В этой системе координат три зеркальные грани тетраэдра будут лежать в координатных плоскостях:</p><p>• Грань $OBC$ лежит в плоскости $x=0$. Вектор нормали к этой плоскости (направленный внутрь тетраэдра) $\vec{n}_x = (1, 0, 0)$.<br>• Грань $OAC$ лежит в плоскости $y=0$. Вектор нормали к этой плоскости $\vec{n}_y = (0, 1, 0)$.<br>• Грань $OAB$ лежит в плоскости $z=0$. Вектор нормали к этой плоскости $\vec{n}_z = (0, 0, 1)$.</p><p>Пусть луч света входит в тетраэдр через основание $ABC$. Обозначим его первоначальный направляющий вектор как $\vec{v} = (v_x, v_y, v_z)$. Луч последовательно отражается от трех зеркальных граней. Порядок отражений не влияет на конечный результат, но для определенности рассмотрим один из возможных порядков.</p><p>Закон отражения света от зеркальной поверхности в векторной форме выглядит следующим образом: если $\vec{v}_{in}$ — направляющий вектор падающего луча, а $\vec{n}$ — единичный вектор нормали к поверхности, то направляющий вектор отраженного луча $\vec{v}_{out}$ определяется формулой:</p><p>$\vec{v}_{out} = \vec{v}_{in} - 2(\vec{v}_{in} \cdot \vec{n})\vec{n}$</p><p>1. <strong>Первое отражение (от грани $OBC$, плоскость $x=0$):</strong></p><p>Падающий луч имеет вектор $\vec{v} = (v_x, v_y, v_z)$. Нормаль к плоскости $\vec{n}_x = (1, 0, 0)$. После отражения вектор направления луча станет $\vec{v}_1$:</p><p>$\vec{v}_1 = \vec{v} - 2(\vec{v} \cdot \vec{n}_x)\vec{n}_x = (v_x, v_y, v_z) - 2(v_x \cdot 1 + v_y \cdot 0 + v_z \cdot 0)(1, 0, 0) = (v_x, v_y, v_z) - 2v_x(1, 0, 0) = (-v_x, v_y, v_z)$.</p><p>После первого отражения компонента вектора скорости, перпендикулярная плоскости отражения, изменила свой знак.</p><p>2. <strong>Второе отражение (от грани $OAC$, плоскость $y=0$):</strong></p><p>Теперь луч с вектором $\vec{v}_1 = (-v_x, v_y, v_z)$ падает на грань с нормалью $\vec{n}_y = (0, 1, 0)$. Новый вектор направления $\vec{v}_2$:</p><p>$\vec{v}_2 = \vec{v}_1 - 2(\vec{v}_1 \cdot \vec{n}_y)\vec{n}_y = (-v_x, v_y, v_z) - 2((-v_x) \cdot 0 + v_y \cdot 1 + v_z \cdot 0)(0, 1, 0) = (-v_x, v_y, v_z) - 2v_y(0, 1, 0) = (-v_x, -v_y, v_z)$.</p><p>Теперь и $y$-компонента вектора изменила знак.</p><p>3. <strong>Третье отражение (от грани $OAB$, плоскость $z=0$):</strong></p><p>Луч с вектором $\vec{v}_2 = (-v_x, -v_y, v_z)$ падает на последнюю грань с нормалью $\vec{n}_z = (0, 0, 1)$. Итоговый вектор направления $\vec{v}_{out}$ после выхода из системы зеркал:</p><p>$\vec{v}_{out} = \vec{v}_2 - 2(\vec{v}_2 \cdot \vec{n}_z)\vec{n}_z = (-v_x, -v_y, v_z) - 2((-v_x) \cdot 0 + (-v_y) \cdot 0 + v_z \cdot 1)(0, 0, 1) = (-v_x, -v_y, v_z) - 2v_z(0, 0, 1) = (-v_x, -v_y, -v_z)$.</p><p>В результате трех отражений от взаимно перпендикулярных плоскостей итоговый направляющий вектор луча $\vec{v}_{out}$ связан с начальным вектором $\vec{v}$ соотношением:</p><p>$\vec{v}_{out} = (-v_x, -v_y, -v_z) = -(v_x, v_y, v_z) = -\vec{v}$.</p><p>Это означает, что вышедший луч параллелен вошедшему, но направлен в противоположную сторону. Таким образом, луч света, войдя в тетраэдр, отразившись от трех зеркальных граней, выйдет через основание в направлении, строго противоположном первоначальному, что и требовалось доказать.</p><p><strong>Ответ:</strong> Утверждение доказано. Введенная система координат и применение векторной формулы закона отражения показывают, что после трех последовательных отражений от взаимно перпендикулярных плоскостей итоговый вектор направления луча $\vec{v}_{out}$ равен $-\vec{v}$, где $\vec{v}$ — начальный вектор направления. Это означает, что луч выходит из тетраэдра параллельно входящему лучу, но в противоположном направлении.</p>"
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            "text" => "<p>Для доказательства воспользуемся координатным методом. Разместим тетраэдр $OABC$ в трехмерной прямоугольной системе координат. Поскольку все плоские углы при вершине $O$ прямые, мы можем совместить вершину $O$ с началом координат $(0, 0, 0)$, а ребра $OA$, $OB$ и $OC$ направить вдоль осей $Ox$, $Oy$ и $Oz$ соответственно.</p><p>В этой системе координат три зеркальные грани тетраэдра будут лежать в координатных плоскостях:</p><p>• Грань $OBC$ лежит в плоскости $x=0$. Вектор нормали к этой плоскости (направленный внутрь тетраэдра) $\vec{n}_x = (1, 0, 0)$.<br>• Грань $OAC$ лежит в плоскости $y=0$. Вектор нормали к этой плоскости $\vec{n}_y = (0, 1, 0)$.<br>• Грань $OAB$ лежит в плоскости $z=0$. Вектор нормали к этой плоскости $\vec{n}_z = (0, 0, 1)$.</p><p>Пусть луч света входит в тетраэдр через основание $ABC$. Обозначим его первоначальный направляющий вектор как $\vec{v} = (v_x, v_y, v_z)$. Луч последовательно отражается от трех зеркальных граней. Порядок отражений не влияет на конечный результат, но для определенности рассмотрим один из возможных порядков.</p><p>Закон отражения света от зеркальной поверхности в векторной форме выглядит следующим образом: если $\vec{v}_{in}$ — направляющий вектор падающего луча, а $\vec{n}$ — единичный вектор нормали к поверхности, то направляющий вектор отраженного луча $\vec{v}_{out}$ определяется формулой:</p><p>$\vec{v}_{out} = \vec{v}_{in} - 2(\vec{v}_{in} \cdot \vec{n})\vec{n}$</p><p>1. <strong>Первое отражение (от грани $OBC$, плоскость $x=0$):</strong></p><p>Падающий луч имеет вектор $\vec{v} = (v_x, v_y, v_z)$. Нормаль к плоскости $\vec{n}_x = (1, 0, 0)$. После отражения вектор направления луча станет $\vec{v}_1$:</p><p>$\vec{v}_1 = \vec{v} - 2(\vec{v} \cdot \vec{n}_x)\vec{n}_x = (v_x, v_y, v_z) - 2(v_x \cdot 1 + v_y \cdot 0 + v_z \cdot 0)(1, 0, 0) = (v_x, v_y, v_z) - 2v_x(1, 0, 0) = (-v_x, v_y, v_z)$.</p><p>После первого отражения компонента вектора скорости, перпендикулярная плоскости отражения, изменила свой знак.</p><p>2. <strong>Второе отражение (от грани $OAC$, плоскость $y=0$):</strong></p><p>Теперь луч с вектором $\vec{v}_1 = (-v_x, v_y, v_z)$ падает на грань с нормалью $\vec{n}_y = (0, 1, 0)$. Новый вектор направления $\vec{v}_2$:</p><p>$\vec{v}_2 = \vec{v}_1 - 2(\vec{v}_1 \cdot \vec{n}_y)\vec{n}_y = (-v_x, v_y, v_z) - 2((-v_x) \cdot 0 + v_y \cdot 1 + v_z \cdot 0)(0, 1, 0) = (-v_x, v_y, v_z) - 2v_y(0, 1, 0) = (-v_x, -v_y, v_z)$.</p><p>Теперь и $y$-компонента вектора изменила знак.</p><p>3. <strong>Третье отражение (от грани $OAB$, плоскость $z=0$):</strong></p><p>Луч с вектором $\vec{v}_2 = (-v_x, -v_y, v_z)$ падает на последнюю грань с нормалью $\vec{n}_z = (0, 0, 1)$. Итоговый вектор направления $\vec{v}_{out}$ после выхода из системы зеркал:</p><p>$\vec{v}_{out} = \vec{v}_2 - 2(\vec{v}_2 \cdot \vec{n}_z)\vec{n}_z = (-v_x, -v_y, v_z) - 2((-v_x) \cdot 0 + (-v_y) \cdot 0 + v_z \cdot 1)(0, 0, 1) = (-v_x, -v_y, v_z) - 2v_z(0, 0, 1) = (-v_x, -v_y, -v_z)$.</p><p>В результате трех отражений от взаимно перпендикулярных плоскостей итоговый направляющий вектор луча $\vec{v}_{out}$ связан с начальным вектором $\vec{v}$ соотношением:</p><p>$\vec{v}_{out} = (-v_x, -v_y, -v_z) = -(v_x, v_y, v_z) = -\vec{v}$.</p><p>Это означает, что вышедший луч параллелен вошедшему, но направлен в противоположную сторону. Таким образом, луч света, войдя в тетраэдр, отразившись от трех зеркальных граней, выйдет через основание в направлении, строго противоположном первоначальному, что и требовалось доказать.</p><p><strong>Ответ:</strong> Утверждение доказано. Введенная система координат и применение векторной формулы закона отражения показывают, что после трех последовательных отражений от взаимно перпендикулярных плоскостей итоговый вектор направления луча $\vec{v}_{out}$ равен $-\vec{v}$, где $\vec{v}$ — начальный вектор направления. Это означает, что луч выходит из тетраэдра параллельно входящему лучу, но в противоположном направлении.</p>"
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№790 (с. 191)
Условие. №790 (с. 191)
скриншот условия
Геометрия, 10-11 класс Учебник, авторы: Атанасян Левон Сергеевич, Бутузов Валентин Фёдорович, Кадомцев Сергей Борисович, Позняк Эдуард Генрихович, Киселёва Людмила Сергеевна, издательство Просвещение, Москва, 2019, коричневого цвета, страница 191, номер 790, Условие

790. Основание ABC тетраэдра ОABC прозрачное, а все остальные грани зеркальные. Все плоские углы при вершине О прямые. Докажите, что луч света, вошедший в тетраэдр через основание ABC под произвольным углом к нему, отразившись от граней, выйдет в противоположном направлении по отношению к входящему лучу. (На этом свойстве основано устройство уголкового отражателя, который, в частности, был запущен на Луну для измерения расстояния до неё с помощью лазера.)

Решение 2. №790 (с. 191)
Геометрия, 10-11 класс Учебник, авторы: Атанасян Левон Сергеевич, Бутузов Валентин Фёдорович, Кадомцев Сергей Борисович, Позняк Эдуард Генрихович, Киселёва Людмила Сергеевна, издательство Просвещение, Москва, 2019, коричневого цвета, страница 191, номер 790, Решение 2
Решение 6. №790 (с. 191)

Для доказательства воспользуемся координатным методом. Разместим тетраэдр $OABC$ в трехмерной прямоугольной системе координат. Поскольку все плоские углы при вершине $O$ прямые, мы можем совместить вершину $O$ с началом координат $(0, 0, 0)$, а ребра $OA$, $OB$ и $OC$ направить вдоль осей $Ox$, $Oy$ и $Oz$ соответственно.

В этой системе координат три зеркальные грани тетраэдра будут лежать в координатных плоскостях:

• Грань $OBC$ лежит в плоскости $x=0$. Вектор нормали к этой плоскости (направленный внутрь тетраэдра) $\vec{n}_x = (1, 0, 0)$.
• Грань $OAC$ лежит в плоскости $y=0$. Вектор нормали к этой плоскости $\vec{n}_y = (0, 1, 0)$.
• Грань $OAB$ лежит в плоскости $z=0$. Вектор нормали к этой плоскости $\vec{n}_z = (0, 0, 1)$.

Пусть луч света входит в тетраэдр через основание $ABC$. Обозначим его первоначальный направляющий вектор как $\vec{v} = (v_x, v_y, v_z)$. Луч последовательно отражается от трех зеркальных граней. Порядок отражений не влияет на конечный результат, но для определенности рассмотрим один из возможных порядков.

Закон отражения света от зеркальной поверхности в векторной форме выглядит следующим образом: если $\vec{v}_{in}$ — направляющий вектор падающего луча, а $\vec{n}$ — единичный вектор нормали к поверхности, то направляющий вектор отраженного луча $\vec{v}_{out}$ определяется формулой:

$\vec{v}_{out} = \vec{v}_{in} - 2(\vec{v}_{in} \cdot \vec{n})\vec{n}$

1. Первое отражение (от грани $OBC$, плоскость $x=0$):

Падающий луч имеет вектор $\vec{v} = (v_x, v_y, v_z)$. Нормаль к плоскости $\vec{n}_x = (1, 0, 0)$. После отражения вектор направления луча станет $\vec{v}_1$:

$\vec{v}_1 = \vec{v} - 2(\vec{v} \cdot \vec{n}_x)\vec{n}_x = (v_x, v_y, v_z) - 2(v_x \cdot 1 + v_y \cdot 0 + v_z \cdot 0)(1, 0, 0) = (v_x, v_y, v_z) - 2v_x(1, 0, 0) = (-v_x, v_y, v_z)$.

После первого отражения компонента вектора скорости, перпендикулярная плоскости отражения, изменила свой знак.

2. Второе отражение (от грани $OAC$, плоскость $y=0$):

Теперь луч с вектором $\vec{v}_1 = (-v_x, v_y, v_z)$ падает на грань с нормалью $\vec{n}_y = (0, 1, 0)$. Новый вектор направления $\vec{v}_2$:

$\vec{v}_2 = \vec{v}_1 - 2(\vec{v}_1 \cdot \vec{n}_y)\vec{n}_y = (-v_x, v_y, v_z) - 2((-v_x) \cdot 0 + v_y \cdot 1 + v_z \cdot 0)(0, 1, 0) = (-v_x, v_y, v_z) - 2v_y(0, 1, 0) = (-v_x, -v_y, v_z)$.

Теперь и $y$-компонента вектора изменила знак.

3. Третье отражение (от грани $OAB$, плоскость $z=0$):

Луч с вектором $\vec{v}_2 = (-v_x, -v_y, v_z)$ падает на последнюю грань с нормалью $\vec{n}_z = (0, 0, 1)$. Итоговый вектор направления $\vec{v}_{out}$ после выхода из системы зеркал:

$\vec{v}_{out} = \vec{v}_2 - 2(\vec{v}_2 \cdot \vec{n}_z)\vec{n}_z = (-v_x, -v_y, v_z) - 2((-v_x) \cdot 0 + (-v_y) \cdot 0 + v_z \cdot 1)(0, 0, 1) = (-v_x, -v_y, v_z) - 2v_z(0, 0, 1) = (-v_x, -v_y, -v_z)$.

В результате трех отражений от взаимно перпендикулярных плоскостей итоговый направляющий вектор луча $\vec{v}_{out}$ связан с начальным вектором $\vec{v}$ соотношением:

$\vec{v}_{out} = (-v_x, -v_y, -v_z) = -(v_x, v_y, v_z) = -\vec{v}$.

Это означает, что вышедший луч параллелен вошедшему, но направлен в противоположную сторону. Таким образом, луч света, войдя в тетраэдр, отразившись от трех зеркальных граней, выйдет через основание в направлении, строго противоположном первоначальному, что и требовалось доказать.

Ответ: Утверждение доказано. Введенная система координат и применение векторной формулы закона отражения показывают, что после трех последовательных отражений от взаимно перпендикулярных плоскостей итоговый вектор направления луча $\vec{v}_{out}$ равен $-\vec{v}$, где $\vec{v}$ — начальный вектор направления. Это означает, что луч выходит из тетраэдра параллельно входящему лучу, но в противоположном направлении.

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