int dx/(sin x * cos x) = int cos x/(sin x * cos^2 x) dx = int cos x/sin x * 1/cos^2 x dx =
= int 1/(sin x/cos x) d(tg x) = int 1/tg x d(tg x) = | t = tg x | = int 1/t dt =
= ln |t| + C = | t = tg x | = ln |tg x| + C