Evaluate $\displaystyle \int \tan^2x\sec^2x\,dx$
I tried several methods:
- First method was I changed $\tan^2x = \sec^2x-1$, and then substitute $\sec x$ to $t$, but it doesn't work.
- Second method was to use substitute $\tan^2x = v$, $\sec x = u$. And, it does not work as well.
Is there any better way to solve this problem?