本刊2011年第3期第33页的例题和2011年第4期第26页的例3都是借助圆的轴对称和同一法证明同一道联赛试题,虽然证法简洁,但对学生而言抽象难懂,不易掌握.现用常规方法给予直接证明.题目(2010年全国数学联赛第二试)已知等腰△ABC中,AB=AC,∠C的平分线与AB边交于点P,M为△ABC的内切圆⊙I与BC边的切点,作MD The third issue of 2011 the third page of 33 examples and 2011 the fourth period of page 26 of the third example are the use of circular axis symmetry and the same method to prove the same league test questions, although the law is simple, but for students Abstraction is difficult to understand, are given a direct proof by conventional methods. Subject (2010 National Mathematics League second test) known isosceles △ ABC, AB = AC, ∠C bisecting line and AB intersect at point P , M is the inscribed circle of △ ABC ⊙I and BC edge of the cut-off point for MD