How do you calculate this

Question

I know it converges, but i need to know the sum of this, i don't know the expression because i'm not English... I need it for my homework and I don't know how to do it, so please if somebody knows how to, I would be glad if he could post it here.

Equation

score 1 · Answer 1 · answered Nov 01 '14 at 12:15

1

Hint: for $\;|x|<1\;,\;\;k\in\Bbb N$ ,

$$\sum_{n=k}^\infty x^n=\frac{x^k}{1-x}$$

answered Nov 01 '14 at 12:15

Timbuc

34,191

I don't know what do you mean, because I was missing from the exercises we had in our school.. so I don't know what any of this means.. – Majky28 Nov 01 '14 at 12:16
1

Sorry to hear that. I guess you will have to fill up the details with the help of one of your teachers or your friends that didn't miss classes. Anyway, the subject here is "(in)finite geometric series". – Timbuc Nov 01 '14 at 12:19

score 0 · Answer 2 · answered Nov 01 '14 at 12:50

0

Hint:

$$\displaystyle \sum_{n=2}^{\infty}\dfrac{20}{2^n} = 20 \times \sum_{n=2}^{\infty}\dfrac{1}{2^n} = 20 \times \left(\frac14+\frac18+\frac1{16}+\cdots\right)$$

answered Nov 01 '14 at 12:50

Henry

157,058

How do you calculate this

2 Answers2