Помогите, пожалуйста, найти интеграл
int x dx/cos^2 (x/2)
Заранее спасибо!!

int x dx/cos^2 (x/2) = | x/2 = t, x = 2 * t, dx = 2 dt | =
= int 2 * t * 2/cos^2 t dt = 4 * int t d(tg t) = 4 * t * tg t - 4 * int tg t dt =
= 4 * t * tg t - 4 * int sin t/cos t dt = 4 * t * tg t - 4 * int 1/cos t d(-cos t) =
= 4 * t * tg t + 4 * int 1/cos t d(cos t) = | cos t = u | =
= 4 * t * tg t + 4 * int 1/u du = 4 * t * tg t + 4 * ln |u| + C = | u = cos t | =
= 4 * t * tg t + 4 * ln |cos t| + C = | t = x/2 | =
= 4 * x/2 * tg (x/2) + 4 * ln |cos (x/2)| + C =
= 2 * x * tg (x/2) + 4 * ln |cos (x/2)| + C

Спасибо