趋向于无穷时,lim{(x^3-2)/(x^3+3)}^x^3=e^limx^3*ln{1-5/(x^3+3)}^x^3=e^limx^3*(-5/x^3)=1/e^5
=lime^(x^3ln(1-5/(x^3+3)))=lime^(-5x^3/(x^3+3))=e^(-5)
