SOLUTION: the 8th term of a G.P is 640.if the first term is 5,find the common ratio and the 10th term

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Question 1172363: the 8th term of a G.P is 640.if the first term is 5,find the common ratio and the 10th term
Answer by ikleyn(52788) About Me  (Show Source):
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The ratio  a%5B8%5D%2Fa%5B1%5D  is equal to  640%2F5 = 128 = 2%5E7.


From the other hand side, the ratio  a%5B8%5D%2Fa%5B1%5D  is  r%5E7.


Therefore,  r = 2 (the common ratio).


Hence,  a%5B10%5D = a%5B1%5D%2Ar%5E9 = 5*512 = 2560.

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