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从近几年的数学竞赛题来看,几何题的比例虽然不大,但出现的题目比较新颖,有一定的难度,运用常规思维往往无法解决,如果换一个角度,从侧面进行思考,问题便化难为易,很快解答出来。一、用比例解例1 右图,长方形面积为35平方厘米,左边直角三角形的面积为5平方厘米,右上角直角三角形的面积为7平方厘米,那么中间三角形(阴影部分)面积是____平方厘米。(1996年小学数学奥林匹克初赛B卷试题) 分析:S_△ABCS_长ABCD=535=17 即:12BE·ABAB·BC=17, 得出:BEBC=27,所以ECBC=57,
In recent years, mathematical contest questions, the proportion of geometric questions, although not large, but the topic is relatively new, there is a certain degree of difficulty, the use of conventional thinking often can not be resolved, if from another perspective, thinking from the side, the problem will be The difficulty is easy, quickly answer it. First, with the right solution Example 1 Right, the rectangular area of 35 square centimeters, the right side of the triangle area of 5 square centimeters, the upper right corner of the right triangle area of 7 square centimeters, then the middle of the triangle (shaded area) is ____ Square centimeter. (Elementary School Mathematical Olympiad in 1996 B test) Analysis: S_ △ ABC S_ long ABCD = 5 35 = 1 7 That is: 1 2BEAB AB BC = 1 7 , Draw: BE BC = 2 7, so EC BC = 5 7,