从函数的表达式判定其在坐标系中的几何特性是中学生的学习难点之一。现行高中教材里在介绍到反函数部分时 ,也就只证明了互为反函数的两个函数图像关于直线 ｙ =ｘ对称。本文介绍另一个更具有启发性的一种证法 ,并沿着其思想方法探索出一般函数 ｙ=ｆ(ｘ)关于直线 ｙ =-ｘ对称 Judging from the function expression of its geometric characteristics in the coordinate system is one of the learning difficulties of high school students. The current high school teaching materials introduced in the part of the inverse function, it is only proved that the two functions of each other inverse function of the image on the line y = x symmetry. This article presents another more instructive one, and explores the general function y = f (x) along its line of thought about the straight line y = -x symmetry