令u = tan(x / 2),dx = 2du / (1+u²)sinx = 2u / (1+u²),cosx = (1 - u²) / (1 + u²)∫ dx / (sinx + cosx)= ∫ 2 / 【(1 + u²) * [2u / (1+u²) + (1 - u²) / (1 + u²)]】 ...