SOLUTION: The sum of first four terms of GP is 30 and that of the last four terms is 960. If the first and last term of GP are 2 and 512 respectively, find the common ratio.
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Question 1062189: The sum of first four terms of GP is 30 and that of the last four terms is 960. If the first and last term of GP are 2 and 512 respectively, find the common ratio. Answer by ikleyn(52790) (Show Source):
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The sum of first four terms of GP is 30 and that of the last four terms is 960. If the first and last term of GP
are 2 and 512 respectively, find the common ratio.
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The sum of the first four terms is
S = . (1)
The sum of the last four terms is
T = = (2)
= =
= (2')
Now divide T by Q (divide (2') by (1)). You will get
= = = , or
32 = , or
= = 8.
Hence, q = 2.
Answer. q = 2.
