有时求动点应满足的几何条件不易得出,也无明显的相关点,但却较容易发现(或经分析可以发现)这个动点的运动常常受到另一个变量的制约,或用这个变量可以将动点(x,y)中的x,y表示出来,我们可以取这个变数为参数,建立轨迹的参数方程,这种方法叫做参数法,如果要得到轨迹的普通方程,需要将参数 Sometimes it is not easy to find the geometry that the motion point should satisfy, nor the obvious correlation point, but it is easier to find (or can be found by analysis). The motion of this motion point is often constrained by another variable or can be used with this variable We can take x and y in the moving point (x, y) as the parameters to establish the parametric equation of the trajectory. This method is called parametric method. If we want to get the ordinary equation of the trajectory, we need to set the parameters