§0-4 dx/（1+根号x） u = 根号x,u^2 = x,dx = 2udu,x = 0,u = 0,x = 4,u = 2§0-4 dx/（1+根号x）= §0-2 1/(1+u) *2udu = §0-2 (2 - 2/(1+u)) du = [2u - 2ln(1+u)] _0-2 = 4 - 2ln3