integral 8/((4x^2+1)^2) dx

I know you have to let x=1/2tanu

therefore dx = 1/2 sec^2 u du

But I get a wrong answer! Somewhere along the way I get messed up.

Also:

integral e^t/(sqrt(e^(2t)+9)) dt from 0 to ln4

Use a substitution like u=e^t to simplify the problem, then let u = 3tant

and so du = 3sec^2t

I also get a wrong answer for this one. Be careful with the limits.