一、教材依据本节教材的安排是从复习向量知识引入,直接利用向量的知识来推导两角差的余弦公式,并单独作为一节.这样安排的用意是突出两角差的余弦公式,本章其他的公式都是由两角差的余弦公式推导出来的,这样,学生学习本章内容时会有一个清晰的思路. First, the textbook based on the textbook arrangement is introduced from the review of vector knowledge, the vector of knowledge directly to derive the cosine formula for the difference between the two corners, and separate as a section .This arrangement is intended to highlight the cosine of the difference between the two corners, this chapter The other formulas are derived from the cosine formula for the difference between the two corners so that students have a clear idea of ​​what to learn in this chapter.