Evaluate: `intsec^6x\ dx`

Explanation

`1+tan^2x = sec^2x `

`I = ∫sec^2x sec^4x dx = ∫sec^2x (1 + tan^2x)2dx`

Put `tan x = t` which means `sec^2xdx = dt`,

` I = int (1+ t^2)^2dt`

`= int(1+t^4+2t^2) dt`

`=tanx+frac{tan^5x}{5}+2frac{tan^3x}{3}`