Номер 981, страница 258 - гдз по алгебре 9 класс учебник Солтан, Солтан

Алгебра, 9 класс Учебник, авторы: Солтан Генадий Николаевич, Солтан Алла Евгеньевна, Жумадилова Аманбала Жумадиловна, издательство Кокшетау, Алматы, 2019

Авторы: Солтан Г. Н., Солтан А. Е., Жумадилова А. Ж.

Тип: Учебник

Издательство: Кокшетау

Год издания: 2019 - 2026

ISBN: 978-601-317-424-2

Рекомендовано Министерством образования и науки Республики Казахстан

Повторение курса алгебры 7-9 классов. Последовательности - номер 981, страница 258.

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            "field_branch_cover" => []
            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1070}
            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1101}
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          #visible: []
          #fillable: []
          #guarded: array:1 [
            0 => "*"
          ]
        }
        1 => App\Models\Branch {#1102
          #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" => 1107681
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
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            "field_branch_order" => null
            "field_url" => null
            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1103
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              #escapeWhenCastingToString: false
            }
            "field_page_start" => "256"
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            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1104
              #items: array:1 [
                0 => App\Models\Book {#1105
                  #connection: "mysql"
                  #table: "books"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
                  #withCount: []
                  +preventsLazyLoading: false
                  #perPage: 15
                  +exists: true
                  +wasRecentlyCreated: false
                  #escapeWhenCastingToString: false
                  #attributes: array:50 [
                    "id" => 4298
                    "created_at" => "2026-04-10 13:58:26"
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                    "field_subject" => Illuminate\Database\Eloquent\Collection {#1106 …2}
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                    "field_publisher" => Illuminate\Database\Eloquent\Collection {#1110 …2}
                    "field_author" => Illuminate\Database\Eloquent\Collection {#1112 …2}
                    "field_author_foreign" => Illuminate\Database\Eloquent\Collection {#1116 …2}
                    "field_book_type" => Illuminate\Database\Eloquent\Collection {#1117 …2}
                    "field_country" => Illuminate\Database\Eloquent\Collection {#1119 …2}
                    "field_city" => Illuminate\Database\Eloquent\Collection {#1121 …2}
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                    "field_level_of_education" => Illuminate\Database\Eloquent\Collection {#1125 …2}
                    "field_standart_of_education" => Illuminate\Database\Eloquent\Collection {#1126 …2}
                    "field_publication_number" => null
                    "field_publication_type" => Illuminate\Database\Eloquent\Collection {#1127 …2}
                    "field_under_the_edition" => Illuminate\Database\Eloquent\Collection {#1128 …2}
                    "field_under_the_edition_degree" => null
                    "field_cover_description" => null
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                    "field_publication_year_until" => null
                    "field_part" => ""
                    "field_part_writing" => ""
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                    "field_for_whom" => "Учебник для учащихся 9 класса общеобразовательных школ"
                    "field_allowed" => "Рекомендовано Министерством образования и науки Республики Казахстан"
                    "field_reserve_field" => null
                    "field_link_to_source" => null
                    "field_tasks_count" => "1291"
                    "field_priority" => "4"
                    "field_default_folder" => "/algebra_09/soltan-u19/"
                    "field_isbn" => "978-601-317-424-2"
                    "field_cover" => array:1 [ …1]
                    "field_cover_alts" => array:1 [ …1]
                    "field_covers" => array:1 [ …1]
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                    "field_recommended_books" => Illuminate\Database\Eloquent\Collection {#1129 …2}
                    "field_new_book" => Illuminate\Database\Eloquent\Collection {#1130 …2}
                    "field_old_book" => Illuminate\Database\Eloquent\Collection {#1131 …2}
                    "field_url" => "/9-klass/algebra/kokshetau-soltan-uchebnik"
                    "field_cover_color" => Illuminate\Database\Eloquent\Collection {#1132 …2}
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                    "field_h1" => null
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                    "breadcrumbs" => array:3 [ …3]
                  ]
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                    "id" => 4298
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                    "field_publisher" => Illuminate\Database\Eloquent\Collection {#1110 …2}
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                    "field_author_foreign" => Illuminate\Database\Eloquent\Collection {#1116 …2}
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                    "field_standart_of_education" => Illuminate\Database\Eloquent\Collection {#1126 …2}
                    "field_publication_number" => null
                    "field_publication_type" => Illuminate\Database\Eloquent\Collection {#1127 …2}
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                    "field_under_the_edition_degree" => null
                    "field_cover_description" => null
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                    "field_publication_year_until" => null
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                    "field_for_whom" => "Учебник для учащихся 9 класса общеобразовательных школ"
                    "field_allowed" => "Рекомендовано Министерством образования и науки Республики Казахстан"
                    "field_reserve_field" => null
                    "field_link_to_source" => null
                    "field_tasks_count" => "1291"
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                    "field_default_folder" => "/algebra_09/soltan-u19/"
                    "field_isbn" => "978-601-317-424-2"
                    "field_cover" => array:1 [ …1]
                    "field_cover_alts" => array:1 [ …1]
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                    "field_recommended_books" => Illuminate\Database\Eloquent\Collection {#1129 …2}
                    "field_new_book" => Illuminate\Database\Eloquent\Collection {#1130 …2}
                    "field_old_book" => Illuminate\Database\Eloquent\Collection {#1131 …2}
                    "field_url" => "/9-klass/algebra/kokshetau-soltan-uchebnik"
                    "field_cover_color" => Illuminate\Database\Eloquent\Collection {#1132 …2}
                    "field_metatags_title" => null
                    "field_metatags_description" => null
                    "field_h1" => null
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                    "breadcrumbs" => array:3 [ …3]
                  ]
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                    0 => "*"
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              ]
              #escapeWhenCastingToString: false
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            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1133
              #items: array:1 [
                0 => App\Models\Branch {#1134
                  #connection: "mysql"
                  #table: "branches"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: true
                  #with: []
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                  #attributes: array:24 [
                    "id" => 1107678
                    "created_at" => "2026-04-10 13:58:26"
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                    "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1135 …2}
                    "field_page_start" => "249"
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                    "book" => Illuminate\Database\Eloquent\Collection {#1136 …2}
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                    "id" => 1107678
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                    "book" => Illuminate\Database\Eloquent\Collection {#1136 …2}
                    "branch_parent" => Illuminate\Database\Eloquent\Collection {#1137 …2}
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                    0 => "*"
                  ]
                }
              ]
              #escapeWhenCastingToString: false
            }
          ]
          #original: array:24 [
            "id" => 1107681
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
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            "field_url" => null
            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1103}
            "field_page_start" => "256"
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            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1104}
            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1133}
          ]
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          ]
        }
      ]
      #escapeWhenCastingToString: false
    }
    "content" => Illuminate\Database\Eloquent\Collection {#1141
      #items: array:3 [
        0 => App\Models\Element {#1150
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          #attributes: array:7 [
            "id" => 1277336
            "created_at" => "2026-04-10 13:58:26"
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            "edition" => Illuminate\Database\Eloquent\Collection {#1159
              #items: array:1 [
                0 => App\Models\Edition {#1151
                  #connection: "mysql"
                  #table: "editions"
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                  #keyType: "int"
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                  #perPage: 15
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                  #escapeWhenCastingToString: false
                  #attributes: array:21 [
                    "id" => 4953
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "title" => "Условие"
                    "field_order" => "1"
                    "field_publisher" => Illuminate\Database\Eloquent\Collection {#1153 …2}
                    "field_content_type" => "free"
                    "field_content_mode" => "text, image"
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                    "field_content_text_checked" => null
                    "field_page_content_text_checked" => "0"
                    "field_solution_author" => "Автор"
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                    "id" => 4953
                    "created_at" => "2026-04-10 13:58:26"
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                    "field_root_dir" => "0-"
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                  ]
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                    0 => "*"
                  ]
                }
              ]
              #escapeWhenCastingToString: false
            }
            "task" => array:2 [
              "refs" => "1108736"
              "type" => "task"
            ]
            "text" => "<p><strong>981.</strong> Сумма $n$ первых членов арифметической прогрессии вычисляется по формуле $S_n = 5n - n^2$. Найдите восьмой член этой прогрессии.</p>"
            "img" => array:1 [
              0 => array:5 [
                "name" => "981-1.jpg"
                "alt" => null
                "width" => "1567"
                "height" => 275
                "path" => "/media/algebra_09/soltan-u19/0-1/981-1.webp?ts=1752834976"
              ]
            ]
          ]
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            "id" => 1277336
            "created_at" => "2026-04-10 13:58:26"
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            "edition" => Illuminate\Database\Eloquent\Collection {#1159}
            "task" => array:2 [
              "refs" => "1108736"
              "type" => "task"
            ]
            "text" => "<p><strong>981.</strong> Сумма $n$ первых членов арифметической прогрессии вычисляется по формуле $S_n = 5n - n^2$. Найдите восьмой член этой прогрессии.</p>"
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                "path" => "/media/algebra_09/soltan-u19/0-1/981-1.webp?ts=1752834976"
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          ]
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            0 => "*"
          ]
        }
        1 => App\Models\Element {#1157
          #connection: "mysql"
          #table: "elements"
          #primaryKey: "id"
          #keyType: "int"
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          #with: []
          #withCount: []
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          #attributes: array:6 [
            "id" => 1278627
            "created_at" => "2026-04-10 13:58:26"
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                0 => App\Models\Edition {#1158
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                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
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                    "field_edition_type" => "solution"
                    "field_root_dir" => "1-"
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                    "field_similar_book" => Illuminate\Database\Eloquent\Collection {#1163 …2}
                    "field_process_formula" => ""
                    "field_edition_group" => Illuminate\Database\Eloquent\Collection {#1164 …2}
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                  ]
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                    "field_solution_author" => "Неизвестный"
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                  +timestamps: true
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                  #hidden: []
                  #visible: []
                  #fillable: []
                  #guarded: array:1 [
                    0 => "*"
                  ]
                }
              ]
              #escapeWhenCastingToString: false
            }
            "task" => array:2 [
              "refs" => "1108736"
              "type" => "task"
            ]
            "img" => array:1 [
              0 => array:5 [
                "name" => "981-1.jpg"
                "alt" => null
                "width" => "1137"
                "height" => 887
                "path" => "/media/algebra_09/soltan-u19/1-1/981-1.webp?ts=1752831826"
              ]
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          ]
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            "id" => 1278627
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "edition" => Illuminate\Database\Eloquent\Collection {#1167}
            "task" => array:2 [
              "refs" => "1108736"
              "type" => "task"
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            "img" => array:1 [
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                "name" => "981-1.jpg"
                "alt" => null
                "width" => "1137"
                "height" => 887
                "path" => "/media/algebra_09/soltan-u19/1-1/981-1.webp?ts=1752831826"
              ]
            ]
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          #changes: []
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          #hidden: []
          #visible: []
          #fillable: []
          #guarded: array:1 [
            0 => "*"
          ]
        }
        2 => App\Models\Element {#1165
          #connection: "mysql"
          #table: "elements"
          #primaryKey: "id"
          #keyType: "int"
          +incrementing: true
          #with: []
          #withCount: []
          +preventsLazyLoading: false
          #perPage: 15
          +exists: true
          +wasRecentlyCreated: false
          #escapeWhenCastingToString: false
          #attributes: array:6 [
            "id" => 1554582
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "edition" => Illuminate\Database\Eloquent\Collection {#1175
              #items: array:1 [
                0 => App\Models\Edition {#1166
                  #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" => 5665
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "title" => "Решение 2 (rus)"
                    "field_order" => "3"
                    "field_publisher" => Illuminate\Database\Eloquent\Collection {#1169 …2}
                    "field_content_type" => "free"
                    "field_content_mode" => "text"
                    "field_page_content_mode" => ""
                    "field_content_text_checked" => null
                    "field_page_content_text_checked" => "0"
                    "field_solution_author" => "Gemini 2.5 Pro"
                    "field_moderator" => "tolik"
                    "field_edition_type" => "solution"
                    "field_root_dir" => "2-"
                    "field_responsible" => Illuminate\Database\Eloquent\Collection {#1170 …2}
                    "field_comment" => null
                    "field_similar_book" => Illuminate\Database\Eloquent\Collection {#1171 …2}
                    "field_process_formula" => "katex"
                    "field_edition_group" => Illuminate\Database\Eloquent\Collection {#1172 …2}
                    "field_content_source" => null
                  ]
                  #original: array:21 [
                    "id" => 5665
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "title" => "Решение 2 (rus)"
                    "field_order" => "3"
                    "field_publisher" => Illuminate\Database\Eloquent\Collection {#1169 …2}
                    "field_content_type" => "free"
                    "field_content_mode" => "text"
                    "field_page_content_mode" => ""
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                    "field_page_content_text_checked" => "0"
                    "field_solution_author" => "Gemini 2.5 Pro"
                    "field_moderator" => "tolik"
                    "field_edition_type" => "solution"
                    "field_root_dir" => "2-"
                    "field_responsible" => Illuminate\Database\Eloquent\Collection {#1170 …2}
                    "field_comment" => null
                    "field_similar_book" => Illuminate\Database\Eloquent\Collection {#1171 …2}
                    "field_process_formula" => "katex"
                    "field_edition_group" => Illuminate\Database\Eloquent\Collection {#1172 …2}
                    "field_content_source" => null
                  ]
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                  #attributeCastCache: []
                  #dateFormat: null
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                  +timestamps: true
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                    0 => "*"
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                }
              ]
              #escapeWhenCastingToString: false
            }
            "task" => array:2 [
              "refs" => "1108736"
              "type" => "task"
            ]
            "text" => "<p>Чтобы найти n-й член арифметической прогрессии ($a_n$), зная формулу суммы её первых n членов ($S_n$), можно использовать формулу $a_n = S_n - S_{n-1}$. Эта формула верна, так как $S_n$ — это сумма всех членов от первого до n-го ($a_1 + a_2 + ... + a_{n-1} + a_n$), а $S_{n-1}$ — это сумма всех членов от первого до (n-1)-го ($a_1 + a_2 + ... + a_{n-1}$). Их разность и будет n-ым членом.<br><br>В задаче требуется найти восьмой член прогрессии, то есть $a_8$. Для этого воспользуемся указанной формулой при $n=8$:<br>$a_8 = S_8 - S_7$<br><br>По условию задачи, формула для суммы n первых членов: $S_n = 5n - n^2$.<br><br>1. Вычислим сумму первых восьми членов ($S_8$), подставив $n=8$ в формулу:<br>$S_8 = 5 \cdot 8 - 8^2 = 40 - 64 = -24$<br><br>2. Вычислим сумму первых семи членов ($S_7$), подставив $n=7$ в формулу:<br>$S_7 = 5 \cdot 7 - 7^2 = 35 - 49 = -14$<br><br>3. Теперь найдем восьмой член прогрессии $a_8$, вычтя $S_7$ из $S_8$:<br>$a_8 = S_8 - S_7 = -24 - (-14) = -24 + 14 = -10$<br><br><strong>Ответ:</strong> -10</p>"
          ]
          #original: array:6 [
            "id" => 1554582
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "edition" => Illuminate\Database\Eloquent\Collection {#1175}
            "task" => array:2 [
              "refs" => "1108736"
              "type" => "task"
            ]
            "text" => "<p>Чтобы найти n-й член арифметической прогрессии ($a_n$), зная формулу суммы её первых n членов ($S_n$), можно использовать формулу $a_n = S_n - S_{n-1}$. Эта формула верна, так как $S_n$ — это сумма всех членов от первого до n-го ($a_1 + a_2 + ... + a_{n-1} + a_n$), а $S_{n-1}$ — это сумма всех членов от первого до (n-1)-го ($a_1 + a_2 + ... + a_{n-1}$). Их разность и будет n-ым членом.<br><br>В задаче требуется найти восьмой член прогрессии, то есть $a_8$. Для этого воспользуемся указанной формулой при $n=8$:<br>$a_8 = S_8 - S_7$<br><br>По условию задачи, формула для суммы n первых членов: $S_n = 5n - n^2$.<br><br>1. Вычислим сумму первых восьми членов ($S_8$), подставив $n=8$ в формулу:<br>$S_8 = 5 \cdot 8 - 8^2 = 40 - 64 = -24$<br><br>2. Вычислим сумму первых семи членов ($S_7$), подставив $n=7$ в формулу:<br>$S_7 = 5 \cdot 7 - 7^2 = 35 - 49 = -14$<br><br>3. Теперь найдем восьмой член прогрессии $a_8$, вычтя $S_7$ из $S_8$:<br>$a_8 = S_8 - S_7 = -24 - (-14) = -24 + 14 = -10$<br><br><strong>Ответ:</strong> -10</p>"
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    "book" => Illuminate\Database\Eloquent\Collection {#1195
      #items: array:1 [
        0 => App\Models\Book {#1147
          #connection: "mysql"
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          #attributes: array:50 [
            "id" => 4298
            "created_at" => "2026-04-10 13:58:26"
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            "field_tree_default_status" => "tasks"
            "field_pages_status" => null
            "field_subject" => Illuminate\Database\Eloquent\Collection {#1140
              #items: array:1 [
                0 => App\Models\Term {#1139
                  #connection: "mysql"
                  #table: "terms"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
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                  #perPage: 15
                  +exists: true
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                  #escapeWhenCastingToString: false
                  #attributes: array:10 [
                    "id" => 6471
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "Алгебра"
                    "field_abbreviated_name" => null
                    "field_cases" => array:6 [ …6]
                    "field_foreign_lang_name" => null
                    "field_short_name" => null
                    "field_subject_type" => "technical_subject"
                    "field_translit" => "algebra"
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                  #original: array:10 [
                    "id" => 6471
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "Алгебра"
                    "field_abbreviated_name" => null
                    "field_cases" => array:6 [ …6]
                    "field_foreign_lang_name" => null
                    "field_short_name" => null
                    "field_subject_type" => "technical_subject"
                    "field_translit" => "algebra"
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              ]
              #escapeWhenCastingToString: false
            }
            "field_class" => Illuminate\Database\Eloquent\Collection {#1146
              #items: array:1 [
                0 => App\Models\Term {#1148
                  #connection: "mysql"
                  #table: "terms"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
                  #withCount: []
                  +preventsLazyLoading: false
                  #perPage: 15
                  +exists: true
                  +wasRecentlyCreated: false
                  #escapeWhenCastingToString: false
                  #attributes: array:6 [
                    "id" => 5458
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "9"
                    "field_cases" => array:6 [ …6]
                    "field_translit" => "devjatyj"
                  ]
                  #original: array:6 [
                    "id" => 5458
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "9"
                    "field_cases" => array:6 [ …6]
                    "field_translit" => "devjatyj"
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                }
              ]
              #escapeWhenCastingToString: false
            }
            "field_publisher" => Illuminate\Database\Eloquent\Collection {#1144
              #items: array:1 [
                0 => App\Models\Term {#1142
                  #connection: "mysql"
                  #table: "terms"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
                  #withCount: []
                  +preventsLazyLoading: false
                  #perPage: 15
                  +exists: true
                  +wasRecentlyCreated: false
                  #escapeWhenCastingToString: false
                  #attributes: array:6 [
                    "id" => 7002
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "Кокшетау"
                    "field_cases" => array:6 [ …6]
                    "field_translit" => "Kokshetau"
                  ]
                  #original: array:6 [
                    "id" => 7002
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "Кокшетау"
                    "field_cases" => array:6 [ …6]
                    "field_translit" => "Kokshetau"
                  ]
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                  #dateFormat: null
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                  +timestamps: true
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                    0 => "*"
                  ]
                }
              ]
              #escapeWhenCastingToString: false
            }
            "field_author" => Illuminate\Database\Eloquent\Collection {#1145
              #items: array:3 [
                0 => App\Models\Term {#1143
                  #connection: "mysql"
                  #table: "terms"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
                  #withCount: []
                  +preventsLazyLoading: false
                  #perPage: 15
                  +exists: true
                  +wasRecentlyCreated: false
                  #escapeWhenCastingToString: false
                  #attributes: array:12 [
                    "id" => 7003
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "Солтан"
                    "field_bio" => null
                    "field_degree_rp" => null
                    "field_foreign_lang_name" => null
                    "field_foreign_lang_patronymic" => null
                    "field_foreign_lang_surname" => null
                    "field_name" => "Генадий"
                    "field_patronymic" => "Николаевич"
                    "field_surname_rp" => null
                  ]
                  #original: array:12 [
                    "id" => 7003
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "Солтан"
                    "field_bio" => null
                    "field_degree_rp" => null
                    "field_foreign_lang_name" => null
                    "field_foreign_lang_patronymic" => null
                    "field_foreign_lang_surname" => null
                    "field_name" => "Генадий"
                    "field_patronymic" => "Николаевич"
                    "field_surname_rp" => null
                  ]
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                  +timestamps: true
                  +usesUniqueIds: false
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                    0 => "*"
                  ]
                }
                1 => App\Models\Term {#1173
                  #connection: "mysql"
                  #table: "terms"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
                  #withCount: []
                  +preventsLazyLoading: false
                  #perPage: 15
                  +exists: true
                  +wasRecentlyCreated: false
                  #escapeWhenCastingToString: false
                  #attributes: array:12 [
                    "id" => 7004
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "Солтан"
                    "field_bio" => null
                    "field_degree_rp" => null
                    "field_foreign_lang_name" => null
                    "field_foreign_lang_patronymic" => null
                    "field_foreign_lang_surname" => null
                    "field_name" => "Алла"
                    "field_patronymic" => "Евгеньевна"
                    "field_surname_rp" => null
                  ]
                  #original: array:12 [
                    "id" => 7004
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "Солтан"
                    "field_bio" => null
                    "field_degree_rp" => null
                    "field_foreign_lang_name" => null
                    "field_foreign_lang_patronymic" => null
                    "field_foreign_lang_surname" => null
                    "field_name" => "Алла"
                    "field_patronymic" => "Евгеньевна"
                    "field_surname_rp" => null
                  ]
                  #changes: []
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                  #attributeCastCache: []
                  #dateFormat: null
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                  #touches: []
                  +timestamps: true
                  +usesUniqueIds: false
                  #hidden: []
                  #visible: []
                  #fillable: []
                  #guarded: array:1 [
                    0 => "*"
                  ]
                }
                2 => App\Models\Term {#1174
                  #connection: "mysql"
                  #table: "terms"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
                  #withCount: []
                  +preventsLazyLoading: false
                  #perPage: 15
                  +exists: true
                  +wasRecentlyCreated: false
                  #escapeWhenCastingToString: false
                  #attributes: array:12 [
                    "id" => 7005
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "Жумадилова"
                    "field_bio" => null
                    "field_degree_rp" => null
                    "field_foreign_lang_name" => null
                    "field_foreign_lang_patronymic" => null
                    "field_foreign_lang_surname" => null
                    "field_name" => "Аманбала"
                    "field_patronymic" => "Жумадиловна"
                    "field_surname_rp" => null
                  ]
                  #original: array:12 [
                    "id" => 7005
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "Жумадилова"
                    "field_bio" => null
                    "field_degree_rp" => null
                    "field_foreign_lang_name" => null
                    "field_foreign_lang_patronymic" => null
                    "field_foreign_lang_surname" => null
                    "field_name" => "Аманбала"
                    "field_patronymic" => "Жумадиловна"
                    "field_surname_rp" => null
                  ]
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                    0 => "*"
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                }
              ]
              #escapeWhenCastingToString: false
            }
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              #items: []
              #escapeWhenCastingToString: false
            }
            "field_book_type" => Illuminate\Database\Eloquent\Collection {#1177
              #items: array:1 [
                0 => App\Models\Term {#1178
                  #connection: "mysql"
                  #table: "terms"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
                  #withCount: []
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                  #perPage: 15
                  +exists: true
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                  #escapeWhenCastingToString: false
                  #attributes: array:10 [
                    "id" => 6671
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "Учебник"
                    "field_book_type_foreign" => null
                    "field_cases" => array:6 [ …6]
                    "field_plural_form" => null
                    "field_short_name" => null
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                    "field_translit" => "uchebnik"
                  ]
                  #original: array:10 [
                    "id" => 6671
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "name" => "Учебник"
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                    "field_cases" => array:6 [ …6]
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                    "field_translit" => "uchebnik"
                  ]
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                  #guarded: array:1 [
                    0 => "*"
                  ]
                }
              ]
              #escapeWhenCastingToString: false
            }
            "field_country" => Illuminate\Database\Eloquent\Collection {#1179
              #items: array:1 [
                0 => App\Models\Term {#1180
                  #connection: "mysql"
                  #table: "terms"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
                  #withCount: []
                  +preventsLazyLoading: false
                  #perPage: 15
                  +exists: true
                  +wasRecentlyCreated: false
                  #escapeWhenCastingToString: false
                  #attributes: array:6 [
                    "id" => 6994
                    "created_at" => "2026-04-10 13:58:26"
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                3 => App\Models\Task {#1411
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№981 (с. 258)
Условие. №981 (с. 258)
скриншот условия
Алгебра, 9 класс Учебник, авторы: Солтан Генадий Николаевич, Солтан Алла Евгеньевна, Жумадилова Аманбала Жумадиловна, издательство Кокшетау, Алматы, 2019, страница 258, номер 981, Условие

981. Сумма $n$ первых членов арифметической прогрессии вычисляется по формуле $S_n = 5n - n^2$. Найдите восьмой член этой прогрессии.

Решение. №981 (с. 258)
Алгебра, 9 класс Учебник, авторы: Солтан Генадий Николаевич, Солтан Алла Евгеньевна, Жумадилова Аманбала Жумадиловна, издательство Кокшетау, Алматы, 2019, страница 258, номер 981, Решение
Решение 2 (rus). №981 (с. 258)

Чтобы найти n-й член арифметической прогрессии ($a_n$), зная формулу суммы её первых n членов ($S_n$), можно использовать формулу $a_n = S_n - S_{n-1}$. Эта формула верна, так как $S_n$ — это сумма всех членов от первого до n-го ($a_1 + a_2 + ... + a_{n-1} + a_n$), а $S_{n-1}$ — это сумма всех членов от первого до (n-1)-го ($a_1 + a_2 + ... + a_{n-1}$). Их разность и будет n-ым членом.

В задаче требуется найти восьмой член прогрессии, то есть $a_8$. Для этого воспользуемся указанной формулой при $n=8$:
$a_8 = S_8 - S_7$

По условию задачи, формула для суммы n первых членов: $S_n = 5n - n^2$.

1. Вычислим сумму первых восьми членов ($S_8$), подставив $n=8$ в формулу:
$S_8 = 5 \cdot 8 - 8^2 = 40 - 64 = -24$

2. Вычислим сумму первых семи членов ($S_7$), подставив $n=7$ в формулу:
$S_7 = 5 \cdot 7 - 7^2 = 35 - 49 = -14$

3. Теперь найдем восьмой член прогрессии $a_8$, вычтя $S_7$ из $S_8$:
$a_8 = S_8 - S_7 = -24 - (-14) = -24 + 14 = -10$

Ответ: -10

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