用乘法则(vu)'=uv'+vu'和链式法则:[v(u(x))]'=v'(u(x))*u'(x)f(x)=x²*e^(ax)f'(x)=e^(ax)*(x²)'+x²*(e^(ax))'=e^(ax)*2x+x²*e^(ax)*(ax)'=2xe^(ax)+ax²e^(ax)=(2+ax)xe^(ax)