Номер 712, страница 205 - 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

IV. Тригонометрия. 27. Формулы тригонометрических функций двойного и половинного углов - номер 712, страница 205.

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                        0 => App\Models\Term {#1118
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                          #table: "terms"
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                            "created_at" => "2026-04-10 13:58:26"
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                        1 => App\Models\Term {#1123
                          #connection: "mysql"
                          #table: "terms"
                          #primaryKey: "id"
                          #keyType: "int"
                          +incrementing: false
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                        2 => App\Models\Term {#1124
                          #connection: "mysql"
                          #table: "terms"
                          #primaryKey: "id"
                          #keyType: "int"
                          +incrementing: false
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                          #withCount: []
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                            "created_at" => "2026-04-10 13:58:26"
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                          #connection: "mysql"
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                            "created_at" => "2026-04-10 13:58:26"
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                    "field_country" => Illuminate\Database\Eloquent\Collection {#1128
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                        0 => App\Models\Term {#1129
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                        0 => App\Models\Term {#1131
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                    "field_popular_book" => null
                    "field_recommended_books" => Illuminate\Database\Eloquent\Collection {#1138}
                    "field_new_book" => Illuminate\Database\Eloquent\Collection {#1139}
                    "field_old_book" => Illuminate\Database\Eloquent\Collection {#1140}
                    "field_url" => "/9-klass/algebra/kokshetau-soltan-uchebnik"
                    "field_cover_color" => Illuminate\Database\Eloquent\Collection {#1141}
                    "field_metatags_title" => null
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                    "breadcrumbs" => array:3 [
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                    0 => "*"
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            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1142
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          ]
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            "id" => 1107662
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            "field_display_title" => "IV. Тригонометрия"
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            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1113}
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            "book" => Illuminate\Database\Eloquent\Collection {#1144}
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        }
        1 => App\Models\Branch {#1143
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            "created_at" => "2026-04-10 13:58:26"
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    "content" => Illuminate\Database\Eloquent\Collection {#1096
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        0 => App\Models\Element {#1085
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            "id" => 1277067
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "edition" => Illuminate\Database\Eloquent\Collection {#1076
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                0 => App\Models\Edition {#1086
                  #connection: "mysql"
                  #table: "editions"
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                    "field_publisher" => Illuminate\Database\Eloquent\Collection {#1080
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                        0 => App\Models\Term {#1084 …30}
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                    "field_comment" => null
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                  ]
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                    0 => "*"
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              ]
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            "task" => array:2 [
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              "type" => "task"
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            "text" => "<p><strong>712.</strong> Найдите значение выражения:</p><p><strong>а)</strong> $8\sin 15^\circ \cdot \cos 15^\circ;$</p><p><strong>б)</strong> $4\sin 22^\circ 30' \cdot \cos 22^\circ 30';$</p><p><strong>в)</strong> $\sin 15^\circ \cdot \cos 15^\circ;$</p><p><strong>г)</strong> $\sin^2 15^\circ - \cos^2 15^\circ;$</p><p><strong>д)</strong> $\sqrt{2} (\cos^2 22.5^\circ - \sin^2 22.5^\circ);$</p><p><strong>е)</strong> $2\tan 15^\circ : (1 - \tan^2 15^\circ).$</p>"
            "img" => array:1 [
              0 => array:5 [
                "name" => "712-1.jpg"
                "alt" => null
                "width" => "1386"
                "height" => 348
                "path" => "/media/algebra_09/soltan-u19/0-1/712-1.webp?ts=1752834710"
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            "id" => 1277067
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "edition" => Illuminate\Database\Eloquent\Collection {#1076}
            "task" => array:2 [
              "refs" => "1108453"
              "type" => "task"
            ]
            "text" => "<p><strong>712.</strong> Найдите значение выражения:</p><p><strong>а)</strong> $8\sin 15^\circ \cdot \cos 15^\circ;$</p><p><strong>б)</strong> $4\sin 22^\circ 30' \cdot \cos 22^\circ 30';$</p><p><strong>в)</strong> $\sin 15^\circ \cdot \cos 15^\circ;$</p><p><strong>г)</strong> $\sin^2 15^\circ - \cos^2 15^\circ;$</p><p><strong>д)</strong> $\sqrt{2} (\cos^2 22.5^\circ - \sin^2 22.5^\circ);$</p><p><strong>е)</strong> $2\tan 15^\circ : (1 - \tan^2 15^\circ).$</p>"
            "img" => array:1 [
              0 => array:5 [
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                "height" => 348
                "path" => "/media/algebra_09/soltan-u19/0-1/712-1.webp?ts=1752834710"
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        }
        1 => App\Models\Element {#1078
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          #table: "elements"
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          #keyType: "int"
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                0 => App\Models\Edition {#1079
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                    "field_edition_group" => Illuminate\Database\Eloquent\Collection {#1103}
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        2 => App\Models\Element {#1102
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                    "created_at" => "2026-04-10 13:58:26"
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                    "title" => "Решение 2 (rus)"
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            "text" => "<p><strong>а)</strong> Для решения используем формулу синуса двойного угла: $ \sin(2\alpha) = 2\sin(\alpha)\cos(\alpha) $.<br>Выражение $ 8\sin 15^\circ \cdot \cos 15^\circ $ можно преобразовать:<br>$ 8\sin 15^\circ \cos 15^\circ = 4 \cdot (2\sin 15^\circ \cos 15^\circ) $.<br>Применяем формулу, где $ \alpha = 15^\circ $:<br>$ 4 \cdot \sin(2 \cdot 15^\circ) = 4 \cdot \sin(30^\circ) $.<br>Так как $ \sin(30^\circ) = \frac{1}{2} $, получаем:<br>$ 4 \cdot \frac{1}{2} = 2 $.<br>Ответ: 2</p><p><strong>б)</strong> Используем ту же формулу синуса двойного угла $ \sin(2\alpha) = 2\sin(\alpha)\cos(\alpha) $.<br>Сначала переведем минуты в градусы: $ 22^\circ30' = 22,5^\circ $.<br>Преобразуем выражение $ 4\sin 22,5^\circ \cdot \cos 22,5^\circ $:<br>$ 4\sin 22,5^\circ \cos 22,5^\circ = 2 \cdot (2\sin 22,5^\circ \cos 22,5^\circ) $.<br>Применяем формулу, где $ \alpha = 22,5^\circ $:<br>$ 2 \cdot \sin(2 \cdot 22,5^\circ) = 2 \cdot \sin(45^\circ) $.<br>Так как $ \sin(45^\circ) = \frac{\sqrt{2}}{2} $, получаем:<br>$ 2 \cdot \frac{\sqrt{2}}{2} = \sqrt{2} $.<br>Ответ: $ \sqrt{2} $</p><p><strong>в)</strong> Снова применяем формулу синуса двойного угла $ \sin(2\alpha) = 2\sin(\alpha)\cos(\alpha) $.<br>Из этой формулы следует, что $ \sin(\alpha)\cos(\alpha) = \frac{1}{2}\sin(2\alpha) $.<br>В нашем случае $ \alpha = 15^\circ $:<br>$ \sin 15^\circ \cos 15^\circ = \frac{1}{2}\sin(2 \cdot 15^\circ) = \frac{1}{2}\sin(30^\circ) $.<br>Так как $ \sin(30^\circ) = \frac{1}{2} $, получаем:<br>$ \frac{1}{2} \cdot \frac{1}{2} = \frac{1}{4} $.<br>Ответ: $ \frac{1}{4} $</p><p><strong>г)</strong> Для решения используем формулу косинуса двойного угла: $ \cos(2\alpha) = \cos^2(\alpha) - \sin^2(\alpha) $.<br>Выражение $ \sin^2 15^\circ - \cos^2 15^\circ $ является противоположным по знаку к формуле косинуса двойного угла:<br>$ \sin^2 15^\circ - \cos^2 15^\circ = -(\cos^2 15^\circ - \sin^2 15^\circ) $.<br>Применяем формулу, где $ \alpha = 15^\circ $:<br>$ - \cos(2 \cdot 15^\circ) = - \cos(30^\circ) $.<br>Так как $ \cos(30^\circ) = \frac{\sqrt{3}}{2} $, получаем:<br>$ -\frac{\sqrt{3}}{2} $.<br>Ответ: $ -\frac{\sqrt{3}}{2} $</p><p><strong>д)</strong> Используем формулу косинуса двойного угла $ \cos(2\alpha) = \cos^2(\alpha) - \sin^2(\alpha) $.<br>В выражении $ \sqrt{2} (\cos^2 22,5^\circ - \sin^2 22,5^\circ) $ часть в скобках соответствует этой формуле при $ \alpha = 22,5^\circ $.<br>$ \cos^2 22,5^\circ - \sin^2 22,5^\circ = \cos(2 \cdot 22,5^\circ) = \cos(45^\circ) $.<br>Подставляем это в исходное выражение:<br>$ \sqrt{2} \cdot \cos(45^\circ) $.<br>Так как $ \cos(45^\circ) = \frac{\sqrt{2}}{2} $, получаем:<br>$ \sqrt{2} \cdot \frac{\sqrt{2}}{2} = \frac{2}{2} = 1 $.<br>Ответ: 1</p><p><strong>е)</strong> Для решения используем формулу тангенса двойного угла: $ \tg(2\alpha) = \frac{2\tg(\alpha)}{1 - \tg^2(\alpha)} $.<br>Выражение $ 2\tg 15^\circ : (1 - \tg^2 15^\circ) $ можно записать в виде дроби:<br>$ \frac{2\tg 15^\circ}{1 - \tg^2 15^\circ} $.<br>Это в точности формула тангенса двойного угла, где $ \alpha = 15^\circ $.<br>$ \tg(2 \cdot 15^\circ) = \tg(30^\circ) $.<br>Значение $ \tg(30^\circ) = \frac{1}{\sqrt{3}} = \frac{\sqrt{3}}{3} $.<br>Ответ: $ \frac{\sqrt{3}}{3} $</p>"
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            "text" => "<p><strong>а)</strong> Для решения используем формулу синуса двойного угла: $ \sin(2\alpha) = 2\sin(\alpha)\cos(\alpha) $.<br>Выражение $ 8\sin 15^\circ \cdot \cos 15^\circ $ можно преобразовать:<br>$ 8\sin 15^\circ \cos 15^\circ = 4 \cdot (2\sin 15^\circ \cos 15^\circ) $.<br>Применяем формулу, где $ \alpha = 15^\circ $:<br>$ 4 \cdot \sin(2 \cdot 15^\circ) = 4 \cdot \sin(30^\circ) $.<br>Так как $ \sin(30^\circ) = \frac{1}{2} $, получаем:<br>$ 4 \cdot \frac{1}{2} = 2 $.<br>Ответ: 2</p><p><strong>б)</strong> Используем ту же формулу синуса двойного угла $ \sin(2\alpha) = 2\sin(\alpha)\cos(\alpha) $.<br>Сначала переведем минуты в градусы: $ 22^\circ30' = 22,5^\circ $.<br>Преобразуем выражение $ 4\sin 22,5^\circ \cdot \cos 22,5^\circ $:<br>$ 4\sin 22,5^\circ \cos 22,5^\circ = 2 \cdot (2\sin 22,5^\circ \cos 22,5^\circ) $.<br>Применяем формулу, где $ \alpha = 22,5^\circ $:<br>$ 2 \cdot \sin(2 \cdot 22,5^\circ) = 2 \cdot \sin(45^\circ) $.<br>Так как $ \sin(45^\circ) = \frac{\sqrt{2}}{2} $, получаем:<br>$ 2 \cdot \frac{\sqrt{2}}{2} = \sqrt{2} $.<br>Ответ: $ \sqrt{2} $</p><p><strong>в)</strong> Снова применяем формулу синуса двойного угла $ \sin(2\alpha) = 2\sin(\alpha)\cos(\alpha) $.<br>Из этой формулы следует, что $ \sin(\alpha)\cos(\alpha) = \frac{1}{2}\sin(2\alpha) $.<br>В нашем случае $ \alpha = 15^\circ $:<br>$ \sin 15^\circ \cos 15^\circ = \frac{1}{2}\sin(2 \cdot 15^\circ) = \frac{1}{2}\sin(30^\circ) $.<br>Так как $ \sin(30^\circ) = \frac{1}{2} $, получаем:<br>$ \frac{1}{2} \cdot \frac{1}{2} = \frac{1}{4} $.<br>Ответ: $ \frac{1}{4} $</p><p><strong>г)</strong> Для решения используем формулу косинуса двойного угла: $ \cos(2\alpha) = \cos^2(\alpha) - \sin^2(\alpha) $.<br>Выражение $ \sin^2 15^\circ - \cos^2 15^\circ $ является противоположным по знаку к формуле косинуса двойного угла:<br>$ \sin^2 15^\circ - \cos^2 15^\circ = -(\cos^2 15^\circ - \sin^2 15^\circ) $.<br>Применяем формулу, где $ \alpha = 15^\circ $:<br>$ - \cos(2 \cdot 15^\circ) = - \cos(30^\circ) $.<br>Так как $ \cos(30^\circ) = \frac{\sqrt{3}}{2} $, получаем:<br>$ -\frac{\sqrt{3}}{2} $.<br>Ответ: $ -\frac{\sqrt{3}}{2} $</p><p><strong>д)</strong> Используем формулу косинуса двойного угла $ \cos(2\alpha) = \cos^2(\alpha) - \sin^2(\alpha) $.<br>В выражении $ \sqrt{2} (\cos^2 22,5^\circ - \sin^2 22,5^\circ) $ часть в скобках соответствует этой формуле при $ \alpha = 22,5^\circ $.<br>$ \cos^2 22,5^\circ - \sin^2 22,5^\circ = \cos(2 \cdot 22,5^\circ) = \cos(45^\circ) $.<br>Подставляем это в исходное выражение:<br>$ \sqrt{2} \cdot \cos(45^\circ) $.<br>Так как $ \cos(45^\circ) = \frac{\sqrt{2}}{2} $, получаем:<br>$ \sqrt{2} \cdot \frac{\sqrt{2}}{2} = \frac{2}{2} = 1 $.<br>Ответ: 1</p><p><strong>е)</strong> Для решения используем формулу тангенса двойного угла: $ \tg(2\alpha) = \frac{2\tg(\alpha)}{1 - \tg^2(\alpha)} $.<br>Выражение $ 2\tg 15^\circ : (1 - \tg^2 15^\circ) $ можно записать в виде дроби:<br>$ \frac{2\tg 15^\circ}{1 - \tg^2 15^\circ} $.<br>Это в точности формула тангенса двойного угла, где $ \alpha = 15^\circ $.<br>$ \tg(2 \cdot 15^\circ) = \tg(30^\circ) $.<br>Значение $ \tg(30^\circ) = \frac{1}{\sqrt{3}} = \frac{\sqrt{3}}{3} $.<br>Ответ: $ \frac{\sqrt{3}}{3} $</p>"
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№712 (с. 205)
Условие. №712 (с. 205)
скриншот условия
Алгебра, 9 класс Учебник, авторы: Солтан Генадий Николаевич, Солтан Алла Евгеньевна, Жумадилова Аманбала Жумадиловна, издательство Кокшетау, Алматы, 2019, страница 205, номер 712, Условие

712. Найдите значение выражения:

а) $8\sin 15^\circ \cdot \cos 15^\circ;$

б) $4\sin 22^\circ 30' \cdot \cos 22^\circ 30';$

в) $\sin 15^\circ \cdot \cos 15^\circ;$

г) $\sin^2 15^\circ - \cos^2 15^\circ;$

д) $\sqrt{2} (\cos^2 22.5^\circ - \sin^2 22.5^\circ);$

е) $2\tan 15^\circ : (1 - \tan^2 15^\circ).$

Решение. №712 (с. 205)
Алгебра, 9 класс Учебник, авторы: Солтан Генадий Николаевич, Солтан Алла Евгеньевна, Жумадилова Аманбала Жумадиловна, издательство Кокшетау, Алматы, 2019, страница 205, номер 712, Решение
Решение 2 (rus). №712 (с. 205)

а) Для решения используем формулу синуса двойного угла: $ \sin(2\alpha) = 2\sin(\alpha)\cos(\alpha) $.
Выражение $ 8\sin 15^\circ \cdot \cos 15^\circ $ можно преобразовать:
$ 8\sin 15^\circ \cos 15^\circ = 4 \cdot (2\sin 15^\circ \cos 15^\circ) $.
Применяем формулу, где $ \alpha = 15^\circ $:
$ 4 \cdot \sin(2 \cdot 15^\circ) = 4 \cdot \sin(30^\circ) $.
Так как $ \sin(30^\circ) = \frac{1}{2} $, получаем:
$ 4 \cdot \frac{1}{2} = 2 $.
Ответ: 2

б) Используем ту же формулу синуса двойного угла $ \sin(2\alpha) = 2\sin(\alpha)\cos(\alpha) $.
Сначала переведем минуты в градусы: $ 22^\circ30' = 22,5^\circ $.
Преобразуем выражение $ 4\sin 22,5^\circ \cdot \cos 22,5^\circ $:
$ 4\sin 22,5^\circ \cos 22,5^\circ = 2 \cdot (2\sin 22,5^\circ \cos 22,5^\circ) $.
Применяем формулу, где $ \alpha = 22,5^\circ $:
$ 2 \cdot \sin(2 \cdot 22,5^\circ) = 2 \cdot \sin(45^\circ) $.
Так как $ \sin(45^\circ) = \frac{\sqrt{2}}{2} $, получаем:
$ 2 \cdot \frac{\sqrt{2}}{2} = \sqrt{2} $.
Ответ: $ \sqrt{2} $

в) Снова применяем формулу синуса двойного угла $ \sin(2\alpha) = 2\sin(\alpha)\cos(\alpha) $.
Из этой формулы следует, что $ \sin(\alpha)\cos(\alpha) = \frac{1}{2}\sin(2\alpha) $.
В нашем случае $ \alpha = 15^\circ $:
$ \sin 15^\circ \cos 15^\circ = \frac{1}{2}\sin(2 \cdot 15^\circ) = \frac{1}{2}\sin(30^\circ) $.
Так как $ \sin(30^\circ) = \frac{1}{2} $, получаем:
$ \frac{1}{2} \cdot \frac{1}{2} = \frac{1}{4} $.
Ответ: $ \frac{1}{4} $

г) Для решения используем формулу косинуса двойного угла: $ \cos(2\alpha) = \cos^2(\alpha) - \sin^2(\alpha) $.
Выражение $ \sin^2 15^\circ - \cos^2 15^\circ $ является противоположным по знаку к формуле косинуса двойного угла:
$ \sin^2 15^\circ - \cos^2 15^\circ = -(\cos^2 15^\circ - \sin^2 15^\circ) $.
Применяем формулу, где $ \alpha = 15^\circ $:
$ - \cos(2 \cdot 15^\circ) = - \cos(30^\circ) $.
Так как $ \cos(30^\circ) = \frac{\sqrt{3}}{2} $, получаем:
$ -\frac{\sqrt{3}}{2} $.
Ответ: $ -\frac{\sqrt{3}}{2} $

д) Используем формулу косинуса двойного угла $ \cos(2\alpha) = \cos^2(\alpha) - \sin^2(\alpha) $.
В выражении $ \sqrt{2} (\cos^2 22,5^\circ - \sin^2 22,5^\circ) $ часть в скобках соответствует этой формуле при $ \alpha = 22,5^\circ $.
$ \cos^2 22,5^\circ - \sin^2 22,5^\circ = \cos(2 \cdot 22,5^\circ) = \cos(45^\circ) $.
Подставляем это в исходное выражение:
$ \sqrt{2} \cdot \cos(45^\circ) $.
Так как $ \cos(45^\circ) = \frac{\sqrt{2}}{2} $, получаем:
$ \sqrt{2} \cdot \frac{\sqrt{2}}{2} = \frac{2}{2} = 1 $.
Ответ: 1

е) Для решения используем формулу тангенса двойного угла: $ \tg(2\alpha) = \frac{2\tg(\alpha)}{1 - \tg^2(\alpha)} $.
Выражение $ 2\tg 15^\circ : (1 - \tg^2 15^\circ) $ можно записать в виде дроби:
$ \frac{2\tg 15^\circ}{1 - \tg^2 15^\circ} $.
Это в точности формула тангенса двойного угла, где $ \alpha = 15^\circ $.
$ \tg(2 \cdot 15^\circ) = \tg(30^\circ) $.
Значение $ \tg(30^\circ) = \frac{1}{\sqrt{3}} = \frac{\sqrt{3}}{3} $.
Ответ: $ \frac{\sqrt{3}}{3} $

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