Номер 487, страница 141 - 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

III. Последовательности. 20. Упражнения на повторение раздела «Последовательности» - номер 487, страница 141.

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            "created_at" => "2026-04-10 13:58:26"
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            "text" => "<p>Для доказательства того, что формула $a_n = 2^n + 1$ верна для последовательности, заданной рекуррентно как $a_1 = 3$ и $a_{n+1} = 2a_n - 1$, воспользуемся методом математической индукции.</p><p>Сначала проверим базу индукции, то есть случай $n=1$. По условию задачи, $a_1 = 3$. Согласно доказываемой формуле, $a_1 = 2^1 + 1 = 2 + 1 = 3$. Так как значения совпадают, база индукции верна.</p><p>Далее, сделаем индукционное предположение. Предположим, что формула верна для некоторого натурального числа $n=k$, то есть $a_k = 2^k + 1$.</p><p>Теперь выполним индукционный переход. Нам нужно доказать, что если формула верна для $n=k$, то она верна и для $n=k+1$. То есть, нужно показать, что $a_{k+1} = 2^{k+1} + 1$. Воспользуемся рекуррентной формулой из условия: $a_{k+1} = 2a_k - 1$. Подставим в неё выражение для $a_k$ из нашего индукционного предположения: $a_{k+1} = 2(2^k + 1) - 1$.</p><p>Раскроем скобки и упростим: $a_{k+1} = 2 \cdot 2^k + 2 \cdot 1 - 1 = 2^{k+1} + 2 - 1 = 2^{k+1} + 1$.</p><p>Мы получили именно то выражение для $a_{k+1}$, которое и требовалось доказать.</p><p>Таким образом, поскольку база индукции верна и индукционный переход доказан, по принципу математической индукции формула $a_n = 2^n + 1$ верна для всех натуральных чисел $n$.</p><p><strong>Ответ:</strong> Что и требовалось доказать.</p>"
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            "text" => "<p>Для доказательства того, что формула $a_n = 2^n + 1$ верна для последовательности, заданной рекуррентно как $a_1 = 3$ и $a_{n+1} = 2a_n - 1$, воспользуемся методом математической индукции.</p><p>Сначала проверим базу индукции, то есть случай $n=1$. По условию задачи, $a_1 = 3$. Согласно доказываемой формуле, $a_1 = 2^1 + 1 = 2 + 1 = 3$. Так как значения совпадают, база индукции верна.</p><p>Далее, сделаем индукционное предположение. Предположим, что формула верна для некоторого натурального числа $n=k$, то есть $a_k = 2^k + 1$.</p><p>Теперь выполним индукционный переход. Нам нужно доказать, что если формула верна для $n=k$, то она верна и для $n=k+1$. То есть, нужно показать, что $a_{k+1} = 2^{k+1} + 1$. Воспользуемся рекуррентной формулой из условия: $a_{k+1} = 2a_k - 1$. Подставим в неё выражение для $a_k$ из нашего индукционного предположения: $a_{k+1} = 2(2^k + 1) - 1$.</p><p>Раскроем скобки и упростим: $a_{k+1} = 2 \cdot 2^k + 2 \cdot 1 - 1 = 2^{k+1} + 2 - 1 = 2^{k+1} + 1$.</p><p>Мы получили именно то выражение для $a_{k+1}$, которое и требовалось доказать.</p><p>Таким образом, поскольку база индукции верна и индукционный переход доказан, по принципу математической индукции формула $a_n = 2^n + 1$ верна для всех натуральных чисел $n$.</p><p><strong>Ответ:</strong> Что и требовалось доказать.</p>"
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                    "created_at" => "2026-04-10 13:58:26"
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                    "edition" => Illuminate\Database\Eloquent\Collection {#1214 …2}
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                2 => App\Models\Task {#1394
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                3 => App\Models\Task {#1411
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№487 (с. 141)
Условие. №487 (с. 141)
скриншот условия
Алгебра, 9 класс Учебник, авторы: Солтан Генадий Николаевич, Солтан Алла Евгеньевна, Жумадилова Аманбала Жумадиловна, издательство Кокшетау, Алматы, 2019, страница 141, номер 487, Условие

487. Последовательность ($a_n$) задана рекуррентно: $a_1 = 3, a_{n+1} = 2a_n - 1$.

Докажите, что $a_n = 2^n + 1$.

Решение. №487 (с. 141)
Алгебра, 9 класс Учебник, авторы: Солтан Генадий Николаевич, Солтан Алла Евгеньевна, Жумадилова Аманбала Жумадиловна, издательство Кокшетау, Алматы, 2019, страница 141, номер 487, Решение
Решение 2 (rus). №487 (с. 141)

Для доказательства того, что формула $a_n = 2^n + 1$ верна для последовательности, заданной рекуррентно как $a_1 = 3$ и $a_{n+1} = 2a_n - 1$, воспользуемся методом математической индукции.

Сначала проверим базу индукции, то есть случай $n=1$. По условию задачи, $a_1 = 3$. Согласно доказываемой формуле, $a_1 = 2^1 + 1 = 2 + 1 = 3$. Так как значения совпадают, база индукции верна.

Далее, сделаем индукционное предположение. Предположим, что формула верна для некоторого натурального числа $n=k$, то есть $a_k = 2^k + 1$.

Теперь выполним индукционный переход. Нам нужно доказать, что если формула верна для $n=k$, то она верна и для $n=k+1$. То есть, нужно показать, что $a_{k+1} = 2^{k+1} + 1$. Воспользуемся рекуррентной формулой из условия: $a_{k+1} = 2a_k - 1$. Подставим в неё выражение для $a_k$ из нашего индукционного предположения: $a_{k+1} = 2(2^k + 1) - 1$.

Раскроем скобки и упростим: $a_{k+1} = 2 \cdot 2^k + 2 \cdot 1 - 1 = 2^{k+1} + 2 - 1 = 2^{k+1} + 1$.

Мы получили именно то выражение для $a_{k+1}$, которое и требовалось доказать.

Таким образом, поскольку база индукции верна и индукционный переход доказан, по принципу математической индукции формула $a_n = 2^n + 1$ верна для всех натуральных чисел $n$.

Ответ: Что и требовалось доказать.

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