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在《相似形》一章的第一单元“比例线段”中,有两个重要的定理及其推论,一个是平行线分线段成比例定理及其推论,另一个是三角形一边的平行线的判定定理.这两个定理是相似形的理论基础.根据前一定理及其推论,由直线平行可以推出线段成比例;根据后一定理,由线段成比例可以推出两直线平行.这就是直线平行与线段成比例之间的内在联系,它为我们提供了证明线段成比例或两直线平行的一种思路.同学们学习这一单元的知识和方法时,一定要理解和掌握直线平行与线段成比例之间这种内在联系及其应用.
In the “Proportional Lines” of the first unit of the chapter “Similarity Shapes”, there are two important theorems and their inferences. One is the proportional theorem and its deduction of parallel line segments, and the other is the determination of parallel lines on one side of a triangle. Theorem. These two theorems are the theoretical foundations of similarity. According to the former theorem and its inference, the straight line can be drawn out in proportion to the line segment; according to the post rationale, the line segment can be proportional to the two straight lines. This is the parallel line between the The intrinsic link between the proportions of the segments gives us a way to prove that the segments are proportional or parallel to each other. When the students learn the knowledge and methods of this unit, they must understand and master the linear parallel to the line segments. This internal connection and its application.