余弦定理是解三角形的重要工具,教材从解三角形的问题出发引导学生探索和证明余弦定理,体现了余弦定理的应用性.余弦定理是勾股定理的推广,那么余弦定理可否从勾股定理出发来进行探索和证明呢?因而笔者对余弦定理的探究和证明做了如下教学设想. The cosine theorem is an important tool to solve the triangle. The textbook guides the students to explore and prove the cosine theorem from the problem of solving the triangle, which shows the applicability of the cosine theorem. The cosine theorem is the generalization of the Pythagorean theorem. Then, can the cosine theorem proceed from the Pythagorean Theorem To explore and prove it? So I on the cosine theorem to explore and prove the following teaching ideas.