# Integral calculation

1. Dec 23, 2008

### kostas

1. The problem statement, all variables and given/known data
Calculate the integral:

$$\int x \frac{dx}{\sqrt{(a^2+x^2)^3}}$$

where $$a\in R$$

2. Relevant equations

3. The attempt at a solution
I solved "similar" integrals like $$\int \frac{dx}{\sqrt{a^2+x^2}}$$

and $$\int \frac{dx}{x(x^2+1)}$$

but none of the approaches I know (and used for the above) seem to work. Not sure how to start here. Any ideas?

2. Dec 23, 2008

### Dick

Just try substituting u=x^2+a^2. Your integral is even easier than the other two.

3. Dec 24, 2008

### kostas

Yes, it was. I was making a silly mistake.

Thanks!