Номер 766, страница 217 - 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. 29. Преобразование произведения тригонометрических функций в сумму и разность - номер 766, страница 217.

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            "text" => "<p><strong>а)</strong> Для вычисления произведения косинусов воспользуемся формулой преобразования произведения в сумму: $ \cos \alpha \cdot \cos \beta = \frac{1}{2}(\cos(\alpha - \beta) + \cos(\alpha + \beta)) $.<br>Подставим значения $\alpha = 45^\circ$ и $\beta = 15^\circ$ в формулу:<br>$ \cos 45^\circ \cdot \cos 15^\circ = \frac{1}{2}(\cos(45^\circ - 15^\circ) + \cos(45^\circ + 15^\circ)) = \frac{1}{2}(\cos 30^\circ + \cos 60^\circ) $.<br>Зная, что $ \cos 30^\circ = \frac{\sqrt{3}}{2} $ и $ \cos 60^\circ = \frac{1}{2} $, получаем:<br>$ \frac{1}{2} \left( \frac{\sqrt{3}}{2} + \frac{1}{2} \right) = \frac{1}{2} \cdot \frac{\sqrt{3} + 1}{2} = \frac{\sqrt{3} + 1}{4} $.<br>Ответ: $ \frac{\sqrt{3} + 1}{4} $.</p><p><strong>б)</strong> Для вычисления произведения синусов используем формулу преобразования произведения в сумму: $ \sin \alpha \cdot \sin \beta = \frac{1}{2}(\cos(\alpha - \beta) - \cos(\alpha + \beta)) $.<br>Подставим значения $\alpha = 105^\circ$ и $\beta = 75^\circ$ в формулу:<br>$ \sin 105^\circ \cdot \sin 75^\circ = \frac{1}{2}(\cos(105^\circ - 75^\circ) - \cos(105^\circ + 75^\circ)) = \frac{1}{2}(\cos 30^\circ - \cos 180^\circ) $.<br>Зная, что $ \cos 30^\circ = \frac{\sqrt{3}}{2} $ и $ \cos 180^\circ = -1 $, получаем:<br>$ \frac{1}{2} \left( \frac{\sqrt{3}}{2} - (-1) \right) = \frac{1}{2} \left( \frac{\sqrt{3}}{2} + 1 \right) = \frac{1}{2} \cdot \frac{\sqrt{3} + 2}{2} = \frac{\sqrt{3} + 2}{4} $.<br>Ответ: $ \frac{\sqrt{3} + 2}{4} $.</p><p><strong>в)</strong> Используем формулу преобразования произведения синусов в сумму: $ \sin \alpha \cdot \sin \beta = \frac{1}{2}(\cos(\alpha - \beta) - \cos(\alpha + \beta)) $.<br>$ 4\sin 37,5^\circ \cdot \sin 7,5^\circ = 4 \cdot \frac{1}{2}(\cos(37,5^\circ - 7,5^\circ) - \cos(37,5^\circ + 7,5^\circ)) = 2(\cos 30^\circ - \cos 45^\circ) $.<br>Зная, что $ \cos 30^\circ = \frac{\sqrt{3}}{2} $ и $ \cos 45^\circ = \frac{\sqrt{2}}{2} $, получаем:<br>$ 2 \left( \frac{\sqrt{3}}{2} - \frac{\sqrt{2}}{2} \right) = 2 \cdot \frac{\sqrt{3} - \sqrt{2}}{2} = \sqrt{3} - \sqrt{2} $.<br>Ответ: $ \sqrt{3} - \sqrt{2} $.</p><p><strong>г)</strong> Используем формулу преобразования произведения синуса на косинус в сумму: $ \sin \alpha \cdot \cos \beta = \frac{1}{2}(\sin(\alpha + \beta) + \sin(\alpha - \beta)) $.<br>$ 8\sin 22,5^\circ \cdot \cos 7,5^\circ = 8 \cdot \frac{1}{2}(\sin(22,5^\circ + 7,5^\circ) + \sin(22,5^\circ - 7,5^\circ)) = 4(\sin 30^\circ + \sin 15^\circ) $.<br>Значение $ \sin 30^\circ = \frac{1}{2} $. Для $ \sin 15^\circ $ используем формулу синуса разности:<br>$ \sin 15^\circ = \sin(45^\circ - 30^\circ) = \sin 45^\circ \cos 30^\circ - \cos 45^\circ \sin 30^\circ = \frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2} - \frac{\sqrt{2}}{2} \cdot \frac{1}{2} = \frac{\sqrt{6} - \sqrt{2}}{4} $.<br>Подставляем значения в выражение:<br>$ 4 \left( \frac{1}{2} + \frac{\sqrt{6} - \sqrt{2}}{4} \right) = 4 \left( \frac{2}{4} + \frac{\sqrt{6} - \sqrt{2}}{4} \right) = 4 \cdot \frac{2 + \sqrt{6} - \sqrt{2}}{4} = 2 + \sqrt{6} - \sqrt{2} $.<br>Ответ: $ 2 + \sqrt{6} - \sqrt{2} $.</p>"
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            "id" => 1554367
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "edition" => Illuminate\Database\Eloquent\Collection {#1116}
            "task" => array:2 [
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              "type" => "task"
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            "text" => "<p><strong>а)</strong> Для вычисления произведения косинусов воспользуемся формулой преобразования произведения в сумму: $ \cos \alpha \cdot \cos \beta = \frac{1}{2}(\cos(\alpha - \beta) + \cos(\alpha + \beta)) $.<br>Подставим значения $\alpha = 45^\circ$ и $\beta = 15^\circ$ в формулу:<br>$ \cos 45^\circ \cdot \cos 15^\circ = \frac{1}{2}(\cos(45^\circ - 15^\circ) + \cos(45^\circ + 15^\circ)) = \frac{1}{2}(\cos 30^\circ + \cos 60^\circ) $.<br>Зная, что $ \cos 30^\circ = \frac{\sqrt{3}}{2} $ и $ \cos 60^\circ = \frac{1}{2} $, получаем:<br>$ \frac{1}{2} \left( \frac{\sqrt{3}}{2} + \frac{1}{2} \right) = \frac{1}{2} \cdot \frac{\sqrt{3} + 1}{2} = \frac{\sqrt{3} + 1}{4} $.<br>Ответ: $ \frac{\sqrt{3} + 1}{4} $.</p><p><strong>б)</strong> Для вычисления произведения синусов используем формулу преобразования произведения в сумму: $ \sin \alpha \cdot \sin \beta = \frac{1}{2}(\cos(\alpha - \beta) - \cos(\alpha + \beta)) $.<br>Подставим значения $\alpha = 105^\circ$ и $\beta = 75^\circ$ в формулу:<br>$ \sin 105^\circ \cdot \sin 75^\circ = \frac{1}{2}(\cos(105^\circ - 75^\circ) - \cos(105^\circ + 75^\circ)) = \frac{1}{2}(\cos 30^\circ - \cos 180^\circ) $.<br>Зная, что $ \cos 30^\circ = \frac{\sqrt{3}}{2} $ и $ \cos 180^\circ = -1 $, получаем:<br>$ \frac{1}{2} \left( \frac{\sqrt{3}}{2} - (-1) \right) = \frac{1}{2} \left( \frac{\sqrt{3}}{2} + 1 \right) = \frac{1}{2} \cdot \frac{\sqrt{3} + 2}{2} = \frac{\sqrt{3} + 2}{4} $.<br>Ответ: $ \frac{\sqrt{3} + 2}{4} $.</p><p><strong>в)</strong> Используем формулу преобразования произведения синусов в сумму: $ \sin \alpha \cdot \sin \beta = \frac{1}{2}(\cos(\alpha - \beta) - \cos(\alpha + \beta)) $.<br>$ 4\sin 37,5^\circ \cdot \sin 7,5^\circ = 4 \cdot \frac{1}{2}(\cos(37,5^\circ - 7,5^\circ) - \cos(37,5^\circ + 7,5^\circ)) = 2(\cos 30^\circ - \cos 45^\circ) $.<br>Зная, что $ \cos 30^\circ = \frac{\sqrt{3}}{2} $ и $ \cos 45^\circ = \frac{\sqrt{2}}{2} $, получаем:<br>$ 2 \left( \frac{\sqrt{3}}{2} - \frac{\sqrt{2}}{2} \right) = 2 \cdot \frac{\sqrt{3} - \sqrt{2}}{2} = \sqrt{3} - \sqrt{2} $.<br>Ответ: $ \sqrt{3} - \sqrt{2} $.</p><p><strong>г)</strong> Используем формулу преобразования произведения синуса на косинус в сумму: $ \sin \alpha \cdot \cos \beta = \frac{1}{2}(\sin(\alpha + \beta) + \sin(\alpha - \beta)) $.<br>$ 8\sin 22,5^\circ \cdot \cos 7,5^\circ = 8 \cdot \frac{1}{2}(\sin(22,5^\circ + 7,5^\circ) + \sin(22,5^\circ - 7,5^\circ)) = 4(\sin 30^\circ + \sin 15^\circ) $.<br>Значение $ \sin 30^\circ = \frac{1}{2} $. Для $ \sin 15^\circ $ используем формулу синуса разности:<br>$ \sin 15^\circ = \sin(45^\circ - 30^\circ) = \sin 45^\circ \cos 30^\circ - \cos 45^\circ \sin 30^\circ = \frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2} - \frac{\sqrt{2}}{2} \cdot \frac{1}{2} = \frac{\sqrt{6} - \sqrt{2}}{4} $.<br>Подставляем значения в выражение:<br>$ 4 \left( \frac{1}{2} + \frac{\sqrt{6} - \sqrt{2}}{4} \right) = 4 \left( \frac{2}{4} + \frac{\sqrt{6} - \sqrt{2}}{4} \right) = 4 \cdot \frac{2 + \sqrt{6} - \sqrt{2}}{4} = 2 + \sqrt{6} - \sqrt{2} $.<br>Ответ: $ 2 + \sqrt{6} - \sqrt{2} $.</p>"
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                    "created_at" => "2026-04-10 13:58:26"
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            "field_publisher" => Illuminate\Database\Eloquent\Collection {#1129
              #items: array:1 [
                0 => App\Models\Term {#1130
                  #connection: "mysql"
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                    "created_at" => "2026-04-10 13:58:26"
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            "field_author" => Illuminate\Database\Eloquent\Collection {#1131
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                  #table: "terms"
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                  #connection: "mysql"
                  #table: "terms"
                  #primaryKey: "id"
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                  #connection: "mysql"
                  #table: "terms"
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                    "name" => "Жумадилова"
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                    "name" => "Учебник"
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                    "name" => "Казахстан"
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№766 (с. 217)
Условие. №766 (с. 217)
скриншот условия
Алгебра, 9 класс Учебник, авторы: Солтан Генадий Николаевич, Солтан Алла Евгеньевна, Жумадилова Аманбала Жумадиловна, издательство Кокшетау, Алматы, 2019, страница 217, номер 766, Условие

766. Вычислите:

а) $ \cos 45^\circ \cdot \cos 15^\circ; $

б) $ \sin 105^\circ \cdot \sin 75^\circ; $

в) $ 4\sin 37,5^\circ \cdot \sin 7,5^\circ; $

г) $ 8\sin 22,5^\circ \cdot \cos 7,5^\circ. $

Решение. №766 (с. 217)
Алгебра, 9 класс Учебник, авторы: Солтан Генадий Николаевич, Солтан Алла Евгеньевна, Жумадилова Аманбала Жумадиловна, издательство Кокшетау, Алматы, 2019, страница 217, номер 766, Решение
Решение 2 (rus). №766 (с. 217)

а) Для вычисления произведения косинусов воспользуемся формулой преобразования произведения в сумму: $ \cos \alpha \cdot \cos \beta = \frac{1}{2}(\cos(\alpha - \beta) + \cos(\alpha + \beta)) $.
Подставим значения $\alpha = 45^\circ$ и $\beta = 15^\circ$ в формулу:
$ \cos 45^\circ \cdot \cos 15^\circ = \frac{1}{2}(\cos(45^\circ - 15^\circ) + \cos(45^\circ + 15^\circ)) = \frac{1}{2}(\cos 30^\circ + \cos 60^\circ) $.
Зная, что $ \cos 30^\circ = \frac{\sqrt{3}}{2} $ и $ \cos 60^\circ = \frac{1}{2} $, получаем:
$ \frac{1}{2} \left( \frac{\sqrt{3}}{2} + \frac{1}{2} \right) = \frac{1}{2} \cdot \frac{\sqrt{3} + 1}{2} = \frac{\sqrt{3} + 1}{4} $.
Ответ: $ \frac{\sqrt{3} + 1}{4} $.

б) Для вычисления произведения синусов используем формулу преобразования произведения в сумму: $ \sin \alpha \cdot \sin \beta = \frac{1}{2}(\cos(\alpha - \beta) - \cos(\alpha + \beta)) $.
Подставим значения $\alpha = 105^\circ$ и $\beta = 75^\circ$ в формулу:
$ \sin 105^\circ \cdot \sin 75^\circ = \frac{1}{2}(\cos(105^\circ - 75^\circ) - \cos(105^\circ + 75^\circ)) = \frac{1}{2}(\cos 30^\circ - \cos 180^\circ) $.
Зная, что $ \cos 30^\circ = \frac{\sqrt{3}}{2} $ и $ \cos 180^\circ = -1 $, получаем:
$ \frac{1}{2} \left( \frac{\sqrt{3}}{2} - (-1) \right) = \frac{1}{2} \left( \frac{\sqrt{3}}{2} + 1 \right) = \frac{1}{2} \cdot \frac{\sqrt{3} + 2}{2} = \frac{\sqrt{3} + 2}{4} $.
Ответ: $ \frac{\sqrt{3} + 2}{4} $.

в) Используем формулу преобразования произведения синусов в сумму: $ \sin \alpha \cdot \sin \beta = \frac{1}{2}(\cos(\alpha - \beta) - \cos(\alpha + \beta)) $.
$ 4\sin 37,5^\circ \cdot \sin 7,5^\circ = 4 \cdot \frac{1}{2}(\cos(37,5^\circ - 7,5^\circ) - \cos(37,5^\circ + 7,5^\circ)) = 2(\cos 30^\circ - \cos 45^\circ) $.
Зная, что $ \cos 30^\circ = \frac{\sqrt{3}}{2} $ и $ \cos 45^\circ = \frac{\sqrt{2}}{2} $, получаем:
$ 2 \left( \frac{\sqrt{3}}{2} - \frac{\sqrt{2}}{2} \right) = 2 \cdot \frac{\sqrt{3} - \sqrt{2}}{2} = \sqrt{3} - \sqrt{2} $.
Ответ: $ \sqrt{3} - \sqrt{2} $.

г) Используем формулу преобразования произведения синуса на косинус в сумму: $ \sin \alpha \cdot \cos \beta = \frac{1}{2}(\sin(\alpha + \beta) + \sin(\alpha - \beta)) $.
$ 8\sin 22,5^\circ \cdot \cos 7,5^\circ = 8 \cdot \frac{1}{2}(\sin(22,5^\circ + 7,5^\circ) + \sin(22,5^\circ - 7,5^\circ)) = 4(\sin 30^\circ + \sin 15^\circ) $.
Значение $ \sin 30^\circ = \frac{1}{2} $. Для $ \sin 15^\circ $ используем формулу синуса разности:
$ \sin 15^\circ = \sin(45^\circ - 30^\circ) = \sin 45^\circ \cos 30^\circ - \cos 45^\circ \sin 30^\circ = \frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2} - \frac{\sqrt{2}}{2} \cdot \frac{1}{2} = \frac{\sqrt{6} - \sqrt{2}}{4} $.
Подставляем значения в выражение:
$ 4 \left( \frac{1}{2} + \frac{\sqrt{6} - \sqrt{2}}{4} \right) = 4 \left( \frac{2}{4} + \frac{\sqrt{6} - \sqrt{2}}{4} \right) = 4 \cdot \frac{2 + \sqrt{6} - \sqrt{2}}{4} = 2 + \sqrt{6} - \sqrt{2} $.
Ответ: $ 2 + \sqrt{6} - \sqrt{2} $.

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