不好意思,计算失误,重新计算了一遍.dy/dt=asint dx/dt=a(1-cost)dy/dx=(dy/dt)/(dx/dt)=sint/(1-cost)d(dy/dx)/dt=(cost-1)/(1-cost)^2(d^2y)/(dx^2)=[d(dy/dx)/dt]/(dx/dt)=[(cost-1)/(1-cost)^2]/a(1-cost)=-1/a(1...