这里就是乘法的求导y=f(x)*g(x)那么y'=f '(x) *g(x) +f(x) *g '(x)y=e^(-x/2) *cos2x那么求导得到y'= [e^(-x/2)]' *cos2x +e^(-x/2) *(cos2x)'= -1/2 *e^(-x/2) *cos2x - 2sin2x *e^(-x/2)