在三角函数的学习过程中,我们不仅要熟记一些常见的三角公式,而且要熟悉其变化形式,尤其是常用公式的变形公式,这对于提高我们思维的灵活性,开拓解题思路,会收到事半功倍的效果．下面通过对二倍角的正余弦公式的 In the learning process of trigonometric functions, we must not only memorize some common triangular formulas, but also be familiar with the forms of its changes, especially the formulas of the commonly used formulas. This will improve the flexibility of our thinking and open up the ideas for solving problems. The effect of doing more with less. The following passes the sine and cosine formula for the double angle