令√x=t
x=t^2
dx=2tdt
∫√x/（1+x）dx
=∫t/(1+t^2)*2tdt
=∫2t^2/(1+t^2)dt
=∫2∫[1-1/(1+t^2)]dt
=2t-2arctant+Cx=0,t=0x=1,t=1原式=0-2+π/4=π/4-2