平面图形翻折的实质是一种旋转变换,本文利用坐标法推导平面图形上两点经翻折后的距离公式,并举例介绍公式的应用。定理如图1,设平面直角坐标系xOy内两点A(x_1,y_1),B(x_2,y_2)(其中y_1>0,y_2<0),若固定半平面x′Oy′x,将半平面xOyx′沿着x′x The essence of the plane figure folding is a kind of rotation transformation. In this paper, the distance formula of the two points on the plane figure is deduced by the coordinate method, and the application of the formula is introduced. Theorem is shown in Fig. 1. Let two points A(x_1,y_1),B(x_2,y_2) (where y_1>0, y_2<0) in the planar rectangular coordinate system xOy be half and half of the fixed half plane x′Oy′x. Plane xOyx’ along x’x