1.本单元重、难点分析本单元的重点是:两角和与差的正弦、余弦、正切公式;二倍角的正弦、余弦、正切公式;运用公式进行简单三角函数式的化简、求值与恒等式证明.本单元的难点有:余弦的和角公式的推导;各公式之间的异同及其内在联系;和角公式、差角公式、倍角公式与以前学过的同 1. The unit’s heavy and difficult analysis The key points of this unit are: sine, cosine and tangent formulas of two angles and difference; sine, cosine and tangent formulae of double angles; simple trigonometric function simplification and evaluation using formulas With the identity, it is proved that the difficulties of this unit are: the derivation of the cosine sum angle formula; the similarities and differences between the formulas and their internal relations; and the angle formula, the difference angle formula, the double angle formula and the previously learned