y=（根号下x+1）（根号下1/x-1）y'=（根号下x+1）'（根号下1/x-1）+（根号下x+1）（根号下1/x-1）' =1/2 （根号下1/x-1）/根号x-1/2 （根号下x+1）/根号x^3 =1/2(1/x-1/根号x）-1/2 （1/x+1/根号x^3)=-1/2(1/根号x+1/根号x^3)=-1/x^2*(x根号x+根号x）
