# Expanding a formula

1. May 19, 2004

### Pattielli

Can you tell me what the following formula will be after it gets expanded ?
$$(1+x+x^2+.......+x^n^-^2+x^n^-^1)^2 = ?$$

Thanks a lot,

Last edited: May 19, 2004
2. May 19, 2004

### Muzza

What's written inside the parantheses is a geometric series. It's equal to (1 - x^(n - 1 + 1)) / (1 - x). Now just square it...

3. May 19, 2004

### Pattielli

Thanks a lot,