my book tells me to make u = sec(x) du = tanxsecx dxwhich makes sense,
but could you also make u = tanx making du = (secx)^2 dx? Mr F says: Yes. And, in my opinion, this is by far the simplest approach to take.
But the latter method is incorrect Mr F says: Says who!?
why? Mr F says: It's not incorrect. In fact, it's better!