∫ (sec(x))^2 * (sec(x))^2 dx
Well.....let's write this in another form
∫ (sec(x)^2 * ((tan(x))^2 + 1 ) dx
Let's split this int o two integrals
∫ (sec(x))^2 * (tan(x)^2 dx + ∫ (sec(x))^2 dx
The second one is easy......we'll come back to it!!
In the first integral, let tan(x) = u
Then, du = (sec(x))^2 dx
So we have
∫ u^2 du =
u^3 / 3 + C =
((tan(x))^3 / 3 + C
The second integral just evaluates to tan(x) + C
So, putting this together, and realizing that C + C is just another constant C, we have
((tan(x))^3 / 3 + tan(x) + C
You can check that this is true by taking the derivative of this......after simplifying, you should get (sec(x))^4 = (sec(x))^2 * (sec(x))^2
Hope this helps.....