本文是作者参照文 [1 ]中的体例撰写的一篇教学案例 ,读来生动、有趣 ,并引人深思 .“案例是教学的窗口 .通过这个窗口 ,可以观察别人的课堂 ,也可以反思自己的实践 .”[1] 我们真诚希望广大中学数学教师能结合本文中“建议讨论的问题”及自己丰富的教学实践 ,对此案例加以研究和反思 ,并进行深层次的点评 .截稿日期 :2 0 0 2年 5月 3 0日 . This article is a teaching case written by the author referring to the style of [1]. It is vivid, interesting, and thought-provoking. “The case is the window of teaching. Through this window, you can observe other people’s classrooms and you can reflect on yourself. Practice.“ [1] We sincerely hope that the majority of middle school mathematics teachers can combine this article’s ”problem and discussion" and their own rich teaching practice to study and reflect on this case and make in-depth comments. Deadline: 2 May 30, 2010.