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“课标”(2011年版)在“图形的相似”中提出掌握一个基本事实:两条直线被一组平行线所截,所得的对应线段成比例(平行线分线段成比例定理).对于这个基本事实,《中小学数学》(初中版)陆续刊登了《对教材中相似三角形判定的再改进》(2010年第9期)、《谈平行线分线段成比例定理形成过程的探究教学》(2010年第10期)、《对一个难以探究的问题的教学》(2010年第12期)、《想当年教学“平行线分线段成比例定理”》(2012年第9期)进行了教学设计探讨.在没有增加“平行线等分线段定理”的情况下,如何进行这个内容的教学?笔者认为借助学生已有的认知经验
“Course Standard ” (2011 Edition) proposes a basic fact in “Similarity in a Graphic ”: the two lines are truncated by a set of parallel lines and the resulting corresponding line segments are proportional (the parallel lines are proportional to the line segments ) For this basic fact, “elementary and middle school mathematics” (junior high school version) published one after another “similar to the text in the triangle to determine the re-improvement” (No. 9 of 2010), “on the parallel line subdivision proportional proportional theorem formation process Teaching in Exploration Teaching ”(No. 10, 2010), Teaching on a Difficult Inquiry (No. 12 of 2010), and Proportional Theorem of Parallel Line Subdivision in Teaching Really Wanting (9 Period) for teaching design.Without increasing “parallel line bisector theorem ”, how to carry out the teaching of this content? I believe that with the students’ existing cognitive experience