anonymous one year ago check my answer? Find S_11 for 1 + 2 + 4 + 8 + ... I got 2047, is that correct?

1. anonymous

wht is "S"?

2. anonymous

I believe that it means the sum of the series

3. anonymous

Write out your equation for me.

5. anonymous

well I know that r=2 and so I multiplied by 2 for each and got 1,2,4,8,16,32,64,128,256,512,1024 and then I looked it up because I wasn't sure what to do next and they got 2047 and I wanted to know how they got that

There is an equation. First you have to find the t11. T11 = term 11.

7. anonymous

The eleventh term is 1024 I believe

8. anonymous

its geometric progression, a, ar, ar^2, ar^3.... the common ratio here is 2, that is, every next term is "previous term multiplied by 2" sum in a GP is given by the formula $\frac{ a (1-r ^{n})}{ 1-r }$

9. anonymous

take a as 1, r as 2 and n as 11

10. anonymous

(1(1-2^11))/1-2 =1-2048/1-2 =2047