s(t)=e^(1-3t)cos(2πt+π／3)v=s(t)'=-3e^(1-3t)cos(2πt+π／3)+e^(1-3t)*[-2πsin(2πt+π／3)]=-3e^(1-3t)cos(2πt+π／3)-2πe^(1-3t)sin(2πt+π／3)t=1/3时v=-3*e^0*(-1)-2πe^0*0=-3*1*-1-0=3