SOLUTION: the sum of a geometric series of 6 terms with ratio 2 is negative 189. what is the first term?

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Question 550239: the sum of a geometric series of 6 terms with ratio 2 is negative 189. what is the first term?
Answer by TutorDelphia(193) About Me  (Show Source):
You can put this solution on YOUR website!
First we need to know the formula of a geometric series:
Its
s=a%28%281-r%5En%29%2F%281-r%29%29
Where s=sum, a=the first term r is the ratio and n is the number of terms
We know most of the info already
-189=a%28%281-2%5E6%29%2F%281-2%29%29
-189=a(1-64)/-1
-189=a%2A-63%2A-1
-189=a%2A63
a=-3
You won't have to do this step, but to get a feel for the series, here's our terms -3,-6,-12,-24,-48,-96 and they do equal -189