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Вопрос по другим предметам:
Найдите сумму 75 первых членов последовательности, общий член который определяется формулой: an=3n-19. Доказать, что-
Автор:
spears
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1. Общий член арифметической прогрессии A(n) определяется по формуле:
An = 3 * n - 19 = -19 + 3 + 3 * (n - 1) = - 16 + 3 * (n - 1);
A1 = -16;
D = 3;
2. Сумма: S75 = (2 * A1 + D * (n - 1)) * n / 2 =
(2 * (-16) + 3 * (75 - 1)) * 75 / 2 = 7125.
Ответ: S75 = 7125.
3. Доказать тождество:
sin20° + sin40° = cos10°;
Применяем формулу разложения суммы на множители:
sin40° + sin20° = 2 * sin((40 + 20) / 2) * cos((40 - 20) / 2) =
2 * sin(60 / 2) * cos(20 / 2) =
2 * sin30° * cos10° = 2 * 0,5 * cos10° = cos10°.
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Вопрос по английскому языку:
Помогите с пересказом текста.
It was Friday evening and shopkeepers in Grimsby came to the Midland Bank to put their money into the night safe . But later that evening the night safe disappeared and with it $ 4,000 . Every Friday evening the shopkeepers put the money they take during the week into the night safe . They don't want leave it in their shops , but the bank closes early . The night safe is outside on the wall and the money they put into it goes into the bank . But on this Friday evening the people who came along the street with their bags full of money dropped them not into a night safe , but into a box that belonged to Mr. Mi chael Bell . Mr. Bell , who makes radios and televisions , had the idea when he saw two men outside the bank one evening . When he came home from work , the two men , who were apparently shopkeepers , were putting some money into the night safe . He made the box at home and painted it . When it was ready , he took it to the bank and hung it on the wall next to the night safe . On the front of the night safe he painted the words : " Please use the new night safe . This one is out of order . " Then he went round the corner and waited for the shopkeepers to arrive . He listened while they dropped their bags money into the box . When it was full , he quickly took it down and went hom with $ 4,000 . Mr. Bell is very clever and his idea was good , but not perfec Now he has time to think of other ideas . He's in prison for stealing .
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Ответов: 1
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3 года назад
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