贵刊83年第4期《一道几何题的补充证法》读后很受启发。该题涉及如下题目: 设ABCD是正方形,M是AB边的中点,MN⊥DM,BN平分∠ABC的外角,用解析法证明:|MD|:|MN|. 该文将题中“M是AB边的中点”的条件减弱为“M是AB边上的任一点”,并给出了证明,但不够全面。本文想就此补充两点。第一,当M取在特殊位置——顶点B时 The 4th edition of the “Complementary Proof of a Geometry Problem” published in the 83rd issue of your magazine was very inspired. This question involves the following topics: Let ABCD be a square, M be the midpoint of the AB side, MN ⊥ DM, BN bisect the outer corner of ∠ ABC, prove by analytical method: |MD|:|MN|. The condition that is the midpoint of the AB side is reduced to “M is any point on the AB side” and the proof is given, but it is not comprehensive enough. This article would like to add two points to this. First, when M is taken at a special position, vertex B