对被积函数放缩即可e^(x^2-x)=e^[(x-1/2)^2-1/4]>=e^(-1/4)e^(x^2-x)<=max{e^(0-0),e^(4-2)}=e^22e^(-1/4)=∫(0,2)e^(-1/4)dx<=∫(0,2)e^(x^2-x)dx<=∫(0,2)e^2dx=2e^2
