原式=lim { [√(x^3+x+1)-x]*[√(x^3+x+1)+x]}/{[x^(3/2)*[√(x^3+x+1)+x]} =lim(x^3-x^2+x+1)/{x^(3/2) [√(x^3+x+1)-x]} =1/1 =1
