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两三角形相似的判定条件，是初中几何重要内容。如能提供不同的证法，作为学生课外兴趣小组的活动材料，则可提高学习兴趣，加深对所学内容的理解。从学生早已知道的“三角形面积等于底乘高之半”出发，可以得到三角形相似判定条件的十分简捷的证法。先提出一个平凡而又有用的命题：命题1若△ABC和△A’B’C’中，∠A
The determination conditions of the two triangles are the important contents of the junior high school geometry. If you can provide different evidence, as a student’s extracurricular interest group activity materials, you can improve the interest in learning and deepen the understanding of what you have learned. From the fact that students already know that “the area of the triangle is equal to the bottom multiplied by the height”, we can get a very simple proof of the triangle’s similarity judgment conditions. First propose a trivial and useful proposition: Proposition 1 If △ABC and △A’B’C’, ∠A