求曲线的轨迹方程是解析几何最基本的课题之一。平面上求曲线方程的方法,归纳起来,大致有以下几种。一、直译法就是通常所说的建标设点、列式、代换、化简这些步骤。例1.设P是⊙O内的一个定点,过P作两条互相垂直的直线交圆于A、B两点。求弦AB中点的轨迹方程。解如图1,取PO所在直线为x轴,O为原点建立直角坐标系。(建标) Finding the trajectory equation of the curve is one of the most basic topics of analytical geometry. The method of finding the curve equation on the plane can be summarized as follows. First, the literal translation method is usually referred to as the establishment of the standard set point, column type, substitution, simplify these steps. Example 1. Let P be a fixed point in ⊙O, cross over P with two perpendicular lines to A, B two points. Find the trajectory equation of the middle point of the string AB. The solution is shown in Figure 1. The straight line where the PO is located is the x-axis, and O is the origin to establish the rectangular coordinate system. (Building bid)