令 y' = P(y),y'' = P * dP/dy原方程化为 y³ * P dP/dy = -1=>2P dP/dy = -2 y^(-3) dy积分：P² = 1/y² + C1, P = ±√(y² + C1) / y=>y dy / √(y² + C1) =±dx积分：√(y&...