# Description of binomial expansion

1. Oct 17, 2011

### squids

what will be the coefficient of the x^n in the expansion of (1+x)^-1 and(1-x)^-1. Please answer it separately..

2. Oct 17, 2011

### grzz

According to the spirit of this forum, an attempt on your part will help to encourage someone to help you.

3. Oct 17, 2011

### squids

i used the general term as tr=C(n,r) a^(n-r)*x^r. however i could not hav a final answer as i supposed this method is not approate so there may be other wayz to solve. and using above formula i always got the answer without the appropriate sign..could anyone help for it..

4. Oct 17, 2011

### grzz

You can use

(1 + x)$^{m}$ = 1 + mx/(1!) + m(m - 1)x$^{2}$/(2!) + ...

5. Oct 17, 2011

### squids

ya i used it but what should be the nth term...i have no idea...pls give me some..

6. Oct 18, 2011

### Ray Vickson

I am sure you have seen the answers to these questions, even before you ever heard of the binomial expansion!

RGV

7. Oct 18, 2011

### HallsofIvy

I believe Ray Vickson is referring to the formula for the infinite geometric sum.