第一部分知识要点相似形的主要内容是；比例、比例线段的概念和性质；相似三角形的定义、性质、判定及其应用．其中平行线分线段成比例定理及其推论是整个内容的基础；相似三角形的性质和判定是整个内容的重点；熟练掌握平行线分线段成比例定理及其推论的应用以及相似三角形的? The main content of the first part of the knowledge points similarity is: the concept and nature of proportions, proportional line segments; the definition, nature, determination and application of similar triangles. The proportional theorem and its inference of the parallel line segment are the basis of the whole content; the nature and judgment of similar triangles are the focus of the whole content; the mastery of proportional theorem of parallel line segment and its application of inference and similar triangles?