# Deriving integral=arctan

1. Oct 15, 2006

### Kalie

Yeah this one is good....

Derive the following:

int(1/(x^2 + a^2)dx = 1/a*arctan(x/a) + C

any idea how I would derive this thing?
Cause I'm totally lost....

2. Oct 15, 2006

### quasar987

Well do you agree that if you show that the derivative of 1/a*arctan(x/a) + C is 1/(x^2 + a^2, then you will have attained your goal?

3. Oct 15, 2006

fundamental theorem of calculus

4. Oct 15, 2006

### Kalie

no he actually wants us to plow thorugh the intregal using subsitution and stuff and then somehow end up at the answer

5. Oct 15, 2006

use the substitution $$x = a\tan \theta$$