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

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

Предыдущий вопрос

Следующий вопрос

Похожие вопросы

Предмет: Русский язык, автор: даша122004

У меня в учебнике вопрос как вы их определили?

2 года назад

Предмет: Русский язык, автор: alenkasuper02

просклонять описываемый портрет ,избираемый делегат

2 года назад

Предмет: Қазақ тiлi, автор: Дана20081

про пингвина на казахском языке текст

2 года назад

Предмет: Математика, автор: lakikrip

решите задачу с помощью уравнения: из посёлка одновременно в разных направлениях выехали два мотоциклиста скорость одного из них было в 1,2 раза меньше скорости другого . С какой скоростью ехал каждый если через 2,4 часа между ними было 158,4 км

8 лет назад

Предмет: Английский язык, автор: SamFireCell

Здравствуйте. помогите расставить правильно плюсы и минусы,

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.
Years passed and finally the day arrived when George was a free man again. At the door of the prison he was given back his old clothes, a small suitcase and his wallet. He walked to the railway station and caught a train back to the small town where he was born and brought up.
After George had got off the train, he came out of the station and looked around him. How everything had changed! There was so much traffic now. What used to be quiet little street was now an enormous supermarket. And next to the supermarket, where there used to be a park, there was now an ugly car park. George couldn’t believe his eyes. All these changes made him feel a bit depressed so he decided to have a cup of tea.
He looked for the old corner café where he used to meet his friends when he was a teenager. But of course it had gone. In its place now stood McDonalds’s, which George had never seen before in his life. He sat down on the hard plastic seat and waited for a waitress to come and take his order. Nobody come. Ten minutes later he realized that he had to go and ask for what he wanted. “A cup of tea, please”, he said. “We don’t make tea, only coffee”, answered the black girl behind the counter. Everything had changed, it seemed. There was nothing here for him anymore.
But as he opened his wallet to pay for the cup of coffee he didn’t really want, he discovered old yellow ticket. He looked at it closely. It was a ticket for a pair of shoes which he had taken to the shoe repairer on the day before the robbery- twenty-five years ago. And of course he hadn’t been able to go back for them.
George left the McDonald’s and walked up High Street, passed what used to be a cinema, but which was now a Leisure Centre (whatever that meant). Then he turned right down a narrow street, and there on the corner was the small shoemaker’s shop. The same little dirty shop was still there, after all these years. George looked in the window and couldn’t believe his eyes, it was the same shoemaker-much older now, of course, with a long white beard. George went into the shop. He suddenly felt very embarrasses when he showed the shoemaker the old yellow ticket.
“Excuse me”, he said. “You won’t remember me. I’ve been away from this town for twenty-five years, but on the day before I left, I gave you a pair of shoes to repair and you gave me this ticket. I know it’s ridiculous, after all these years but I wonder if…”
The shoemaker took the old yellow ticket, looked at it closely and then disappeared to the back of the shop. A few minutes later he came back.
“Was it a pair of black shoes?”-he asked.
“Yes”, said George excitedly.
“A pair of black shoes, size eight and a half?”
“Yes”, said George.
“Needed new heels?”, asked the shoemaker.
“Yes, that’s right! You mean you’ve got them?”
“Oh, yes. I’ve still got them”, said the shoemaker. “They will be ready on Friday”.

8 лет назад