Номер 412, страница 120 - 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. 16. Сумма n первых членов арифметической прогрессии - номер 412, страница 120.

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            "created_at" => "2026-04-10 13:58:26"
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            "edition" => Illuminate\Database\Eloquent\Collection {#1175
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                    "created_at" => "2026-04-10 13:58:26"
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            "task" => array:2 [
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            "text" => "<p>Для нахождения значения данного выражения сгруппируем слагаемые попарно:</p><p>$S = (25^2 - 24^2) + (23^2 - 22^2) + \dots + (3^2 - 2^2) + 1^2$</p><p>Применим к каждой скобке формулу разности квадратов: $a^2 - b^2 = (a-b)(a+b)$.</p><p>$(25^2 - 24^2) = (25-24)(25+24) = 1 \cdot 49 = 49$</p><p>$(23^2 - 22^2) = (23-22)(23+22) = 1 \cdot 45 = 45$</p><p>И так далее для всех пар. Последняя пара:</p><p>$(3^2 - 2^2) = (3-2)(3+2) = 1 \cdot 5 = 5$</p><p>Теперь исходная сумма принимает вид:</p><p>$S = 49 + 45 + 41 + \dots + 5 + 1$</p><p>Мы получили сумму членов арифметической прогрессии. Для удобства вычислений запишем ее в порядке возрастания:</p><p>$S = 1 + 5 + 9 + \dots + 45 + 49$</p><p>Это арифметическая прогрессия, у которой:</p><p>Первый член $a_1 = 1$.</p><p>Последний член $a_n = 49$.</p><p>Разность прогрессии $d = 5 - 1 = 4$.</p><p>Найдем количество членов $n$ в этой прогрессии, используя формулу n-го члена $a_n = a_1 + (n-1)d$:</p><p>$49 = 1 + (n-1) \cdot 4$</p><p>$48 = (n-1) \cdot 4$</p><p>$n-1 = \frac{48}{4}$</p><p>$n-1 = 12$</p><p>$n = 13$</p><p>Таким образом, в прогрессии 13 членов. Теперь найдем сумму этой прогрессии по формуле $S_n = \frac{a_1 + a_n}{2} \cdot n$:</p><p>$S = \frac{1 + 49}{2} \cdot 13$</p><p>$S = \frac{50}{2} \cdot 13$</p><p>$S = 25 \cdot 13$</p><p>$S = 325$</p><p><strong>Ответ:</strong> 325</p>"
          ]
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            "id" => 1554013
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            "task" => array:2 [
              "refs" => "1108137"
              "type" => "task"
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            "text" => "<p>Для нахождения значения данного выражения сгруппируем слагаемые попарно:</p><p>$S = (25^2 - 24^2) + (23^2 - 22^2) + \dots + (3^2 - 2^2) + 1^2$</p><p>Применим к каждой скобке формулу разности квадратов: $a^2 - b^2 = (a-b)(a+b)$.</p><p>$(25^2 - 24^2) = (25-24)(25+24) = 1 \cdot 49 = 49$</p><p>$(23^2 - 22^2) = (23-22)(23+22) = 1 \cdot 45 = 45$</p><p>И так далее для всех пар. Последняя пара:</p><p>$(3^2 - 2^2) = (3-2)(3+2) = 1 \cdot 5 = 5$</p><p>Теперь исходная сумма принимает вид:</p><p>$S = 49 + 45 + 41 + \dots + 5 + 1$</p><p>Мы получили сумму членов арифметической прогрессии. Для удобства вычислений запишем ее в порядке возрастания:</p><p>$S = 1 + 5 + 9 + \dots + 45 + 49$</p><p>Это арифметическая прогрессия, у которой:</p><p>Первый член $a_1 = 1$.</p><p>Последний член $a_n = 49$.</p><p>Разность прогрессии $d = 5 - 1 = 4$.</p><p>Найдем количество членов $n$ в этой прогрессии, используя формулу n-го члена $a_n = a_1 + (n-1)d$:</p><p>$49 = 1 + (n-1) \cdot 4$</p><p>$48 = (n-1) \cdot 4$</p><p>$n-1 = \frac{48}{4}$</p><p>$n-1 = 12$</p><p>$n = 13$</p><p>Таким образом, в прогрессии 13 членов. Теперь найдем сумму этой прогрессии по формуле $S_n = \frac{a_1 + a_n}{2} \cdot n$:</p><p>$S = \frac{1 + 49}{2} \cdot 13$</p><p>$S = \frac{50}{2} \cdot 13$</p><p>$S = 25 \cdot 13$</p><p>$S = 325$</p><p><strong>Ответ:</strong> 325</p>"
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            "field_class" => Illuminate\Database\Eloquent\Collection {#1146
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                    "id" => 5458
                    "created_at" => "2026-04-10 13:58:26"
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                    "name" => "9"
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                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
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                    "field_translit" => "Kokshetau"
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            "field_author" => Illuminate\Database\Eloquent\Collection {#1145
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                  #table: "terms"
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                    "created_at" => "2026-04-10 13:58:26"
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                    "created_at" => "2026-04-10 13:58:26"
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                2 => App\Models\Term {#1174
                  #connection: "mysql"
                  #table: "terms"
                  #primaryKey: "id"
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                    "created_at" => "2026-04-10 13:58:26"
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                    "created_at" => "2026-04-10 13:58:26"
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№412 (с. 120)
Условие. №412 (с. 120)
скриншот условия
Алгебра, 9 класс Учебник, авторы: Солтан Генадий Николаевич, Солтан Алла Евгеньевна, Жумадилова Аманбала Жумадиловна, издательство Кокшетау, Алматы, 2019, страница 120, номер 412, Условие

412. Найдите сумму $25^2 - 24^2 + 23^2 - 22^2 + ... - 2^2 + 1^2$.

Решение. №412 (с. 120)
Алгебра, 9 класс Учебник, авторы: Солтан Генадий Николаевич, Солтан Алла Евгеньевна, Жумадилова Аманбала Жумадиловна, издательство Кокшетау, Алматы, 2019, страница 120, номер 412, Решение
Алгебра, 9 класс Учебник, авторы: Солтан Генадий Николаевич, Солтан Алла Евгеньевна, Жумадилова Аманбала Жумадиловна, издательство Кокшетау, Алматы, 2019, страница 120, номер 412, Решение (продолжение 2)
Решение 2 (rus). №412 (с. 120)

Для нахождения значения данного выражения сгруппируем слагаемые попарно:

$S = (25^2 - 24^2) + (23^2 - 22^2) + \dots + (3^2 - 2^2) + 1^2$

Применим к каждой скобке формулу разности квадратов: $a^2 - b^2 = (a-b)(a+b)$.

$(25^2 - 24^2) = (25-24)(25+24) = 1 \cdot 49 = 49$

$(23^2 - 22^2) = (23-22)(23+22) = 1 \cdot 45 = 45$

И так далее для всех пар. Последняя пара:

$(3^2 - 2^2) = (3-2)(3+2) = 1 \cdot 5 = 5$

Теперь исходная сумма принимает вид:

$S = 49 + 45 + 41 + \dots + 5 + 1$

Мы получили сумму членов арифметической прогрессии. Для удобства вычислений запишем ее в порядке возрастания:

$S = 1 + 5 + 9 + \dots + 45 + 49$

Это арифметическая прогрессия, у которой:

Первый член $a_1 = 1$.

Последний член $a_n = 49$.

Разность прогрессии $d = 5 - 1 = 4$.

Найдем количество членов $n$ в этой прогрессии, используя формулу n-го члена $a_n = a_1 + (n-1)d$:

$49 = 1 + (n-1) \cdot 4$

$48 = (n-1) \cdot 4$

$n-1 = \frac{48}{4}$

$n-1 = 12$

$n = 13$

Таким образом, в прогрессии 13 членов. Теперь найдем сумму этой прогрессии по формуле $S_n = \frac{a_1 + a_n}{2} \cdot n$:

$S = \frac{1 + 49}{2} \cdot 13$

$S = \frac{50}{2} \cdot 13$

$S = 25 \cdot 13$

$S = 325$

Ответ: 325

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