# A textbook problem

1. Oct 28, 2005

### Swatch

I have a textbook problem I am trying to solve with no luck.
I know 1/(u^2 -1) = 1/2 [ 1/(u-1) - 1/(u+1) ]
I come so far to see that 1/(u^2 -1) = 1/ [(u-1)(u+1) ]
But I don't know what comes next. Could somebody please give me a hint.

2. Oct 28, 2005

### Physics Monkey

Hint: This is called partial fraction decomposition, and you can think of it as the opposite of finding a common denominator.

3. Oct 28, 2005

### TD

Well you factored your denominator correctly. Now try to work the other way arround. "Suppose" you can split your fraction into two parts, and then try to find the right coefficients. So suppose that:

$$\frac{1}{{u^2 - 1}} = \frac{A}{{u - 1}} + \frac{B}{{u + 1}}$$

Now try to find A and B.

4. Oct 29, 2005

### Swatch

Thanks, it worked.