Evaluate the following integrals `int_0^(pi/4)tan^2xdx`

Explanation

`int_0^(pi/4)tan^2xdx=int_0^(pi/4)(sec^2 x-1)dx`
`[tanx-x]_o^(pi/4)`
`tan(pi/4)-(pi/4)=(4-pi)/4`