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## anonymous 4 years ago What is the sum of the geometric sequence 8, –16, 32 … if there are 15 terms?

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1. anonymous

$a\frac{(1-r^{n+1})}{(1-r)}$

2. anonymous

so would it be 87384?

3. anonymous

$\sum _{n=0}^{15} (8)(-2)^n$ $8\sum _{n=0}^{14} (-2)^n$ 8((1-(-2)^15))/(1+2) http://www.wolframalpha.com/input/?i=8%28%281-%28-2%29%5E15%29%29%2F%281%2B2%29 yes

4. anonymous

wanna do some more for me? :)

5. anonymous

no, I think you can handle it

6. anonymous

I don't think so

7. anonymous

yes, you got the right answer

8. anonymous

i googled it... i wanted to see if it was correct

9. anonymous

do some more , you will get the hang of it

10. anonymous

Thanks.

11. anonymous

and if you get stuck , post it ; you will be helped

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