SOLUTION: The sum of the first 8 terms of a geometrical series is 17 times the sum of its first 4 terms. Find the common ratio. This is the equation I have come up with (a is first term,

Algebra ->  Sequences-and-series -> SOLUTION: The sum of the first 8 terms of a geometrical series is 17 times the sum of its first 4 terms. Find the common ratio. This is the equation I have come up with (a is first term,       Log On


   

Question 1146283: The sum of the first 8 terms of a geometrical series is 17 times the sum of its first 4 terms. Find the common ratio.
This is the equation I have come up with (a is first term, r is common ratio):
%28a%28r%5E8-1%29%29%2F%28r-1%29+=+%2817a%28r%5E4-1%29%29%2F%28r-1%29
But I don't really know how to solve it.
Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!


In your equation, the "a" in the numerator and the "r-1" in the denominator are the same, so the equation simplifies to

%28r%5E8-1%29+=+17%28r%5E4-1%29

Then on the left note that

r%5E8-1+=+%28r%5E4%2B1%29%28r%5E4-1%29

That should lead you quickly to TWO solutions to the problem.