分成两个积分
∫[1,2](√x+1)/x^2 dx
=∫[1,2]x^(-3/2) dx+ ∫[1,2](1/x^2) dx
=[-2*x^(-1/2)-1/x][1,2]
=- √2-1/2+2+1
= 5/2-√2