第二十六届IMO第五题是一道优秀的平面几何题,一般的证法使用根轴,本文的证法比较简捷,在引伸和发展中,这种证法也基本适用。下面我们先证明这个问题,然后引伸和发展这个问题。圆O经过△ABC的顶点A和C,且与边AB、BC分别交于k和N,K与N不同,△ABC与△BKN的外接圆相交于B和另一点M,求 The twenty-sixth session of the IMO fifth question is an excellent plane geometry problem. The general verification method uses the root axis. The verification method of this article is relatively simple. In the extension and development, this type of verification method is also basically applicable. Here we first prove this problem, and then extend and develop this problem. The circle O passes through the vertices A and C of △ABC, and intersects with the sides AB and BC respectively at k and N. K and N are different, and the circumscribed circle of △ABC and △BKN intersects at B and at another point M.