Integrate `sec^(3) ` x w.r.t.x.

Explanation

`int sec^(3) x dx = int sec x sec ^(2) x dx `
` = sec x tan x - int tan x sec x tan x dx `
`[:' tan^(2) x = sec^(2) x -1]`
` = sec x tan x - int sec x (sec ^(2) x -1) dx `
` = sec x tan x + int sec x dx - int sec^(3) x dx `
or ` 2 int sec^(3) x dx = sec x tan x + log | sec x + tan x | + c`
or ` int sec^(3) x dx = 1/2 sec x tan x + 1/2 log | sec x + tan x | +c `