延长CM交⊙O于F∵AB是圆O的直径∴AC⊥BD,（那么多相似三角形我不全证了）∵CE*CF=CD*AC（割线定理）,CE=CM-ME,CF=CM+ME∴(CM-ME)*(CM+ME)=CD*AC,即CM²-ME²=CD*AC又∵△CDN∽△CMA（因为∠C=∠C,∠CDN=∠CM...