令p=dy/dx, 则d^2y/dx^2=dp/dy*dy/dx=pdp/dy
代入原方程：pdp/dy=Acosy
即pdp=Acosydy
积分：p^2/2=Asiny+C1
得：p=±√[2Asiny+C]
dy/√[2Asiny+C]=±dx
积分得：∫dy/√[2Asiny+C]=±x+C1