Originally Posted by
ticbol The Pythagorean trig identity:
sin^2(A) +cos^2(A) = 1
Divide both sides by cos^2(A),
tan^2(A) +1 = sec^2(A)
tan^2(A) = sec^2(A) -1 --------------(i)
So,
INT.[tan^2(x)]dx
= INT.[sec^2(x) -1]dx
= tan(x) -x +C -------------------answer.