int u/(u^2 - 1) du = int d(1/2 * u^2)/(u^2 - 1) = 1/2 * int d(u^2)/(u^2 - 1) =
= 1/2 * int d(u^2 - 1)/(u^2 - 1) = | t = u^2 - 1 | = 1/2 * int dt/t =
= 1/2 * ln |t| + C = | t = u^2 - 1 | = 1/2 * ln |u^2 - 1| + C