答：设t=√x,x=t^2
∫[1/(√x+x)]dx
=∫[1/(t+t^2)] d(t^2)
=∫[1/(t+t^2)] 2tdt
=2∫[1/(1+t)] d(t+1)
=2ln(t+1)+C
=2ln(√x+1)+C