Evaluate: `intsin^2x dx`

Explanation

`int tan^(4)xdx=int tan^(2)x tan^(2)xdx=int tan^(2)x(sec^(2)x-1)dx`
`=int tan^(2)x sec^(2)xdx-int tan^(2)xdx=(sec^(3)x)/(3)-int(sec^(2)x-1)dx`
`=(sec^(3)x)/(3)-tanx+x+C`