SOLUTION: i) Find the first term of the geometric progression with r=-5 if the sum of the first 6 terms is 2604.

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Question 1023902: i) Find the first term of the geometric progression with r=-5 if the sum of the first 6 terms is 2604.
(ii) Write down the first 6 terms of the geometric progression in (i) above.
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
(i) The formula for the sum of the first n terms of a GP is S%5Bn%5D+=+g%5B1%5D%2A%28%281-r%5En%29%2F%281-r%29%29
==> 2604+=+g%5B1%5D%2A%28%281-%28-5%29%5E6%29%2F%281--5%29%29
==> 15624+=+g%5B1%5D%28-15624%29 ==> g%5B1%5D+=+-1
(ii) The first six terms are -1, 5, -25, 125, -625, 3125.