大家知道,在直角坐标系中,过定点P(x_0,y_0)且倾斜角为α的直线l的参数方程为{x=x_0+tcosα,y=y_0+tsinα(其中t为参数).我们不妨称它为直线参数方程的标准形式,其中|t|表示直线l上的任意点A到定点P(x_0,y_0)的距离,即|PA|=|t|,t等于有向线段PA的长.当A在P的上方或右边时t为正, We know that in the Cartesian coordinate system, the parameter equation of the straight line l passing through the point P (x_0, y_0) and the tilt angle α is {x = x_0 + tcosα, y = y_0 + tsinα (where t is the parameter). It is called the standard form of the linear parameter equation, where | t | denotes the distance from any point A on the straight line l to the fixed point P (x_0, y_0), ie | PA | = | t |, t is equal to the length of the directed segment PA T is positive when A is above or to the right of P,