Предмет: Алгебра, автор: Jigsaw

В геометрической прогрессии а7=-14. Найдите а5*а9 Пожалуйста, с решением

Ответы

Автор ответа: ТатМих

В геометрической прогрессии все члены обозначаются как b
Формула n -го члена прогрессии
$bn=b1* q^{n-1}$
b1-первый член прогрессии
n-количество членов
q -знаменатель прогрессии

$bn=b1* q^{n-1} \\ \\ b7=b1* q^{6} =-14 \\ b5=b1*q^4 \\ b9=b1*q^8 \\ \\ b5*b9=b1*b1*(q^4*q^8) \\ \\ =(b1)^2* q^{12} = (b1*q^{6} )^2 \\ \\ =(b7)^2=(-14)^2=196$

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A Shoemaker’s shop
One afternoon many years ago, George Cox robbed Barcleys Bank. He stole over 50.000 pounds. But unfortunately, when he came out of the bank, the police were waiting for him. George was arrested and sentenced to 25 years in prison.
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