∫ln(x+√(1+x^2))dx
=xln(x+√(1+x^2) -∫xd(ln(x+√(1+x^2))
=xln(x+√(1+x^2)-∫xdx/√(1+x^2)
=xln(x+√(1+x^2)-(1/2)∫d(1+x^2)/√(1+x^2)
=xln(x+√(1+x^2)-√(1+x^2)+C朋友，看不懂啊！第一步怎么到第二步分部积分