图为质点的正弦函数：H=Vm*sin(x+1/6π)则其余弦为：H=Vm*cos(0.5π-(x+1/6π))=Vm*cos(-x+1/3π)=Vm*cos(x-1/3π)
简谐振动速度方程v=Aωcos(ωt+a)vm=Aωt=0 时 v=（1/2)vm=vmcosacosa =1/2 a=±π/6 由图可见 初位相角取 a=-π/6 (A)
A
cosa =1/2 a=±π/6 ？你看看对吗？
