将某些例题、习题以及某些概念、性质延伸后得到的结论我们称之为引申公式.注意这些引申公式可使某些问题的求解变得简单. 1.三角中的引申公式 (1)三角中的平方差公式 sin2α-sin2β=sin(α+β)sin(α-β),从左往右用,可将平方差化积;从右往左用,可将乘积化成平方差. 例1 (sin280°-sin240°)/(cos280°-sin240°)=( ) The conclusions obtained by extending some examples, exercises, and some concepts and properties are called extended formulas. Note that these extended formulas can make the solution of certain problems simple. 1. Extended formulas in triangles (1) Triangles The squared difference formula in sin2α-sin2β=sin(α+β)sin(α-β), which can be used from left to right to square the difference product; from right to left, the product can be transformed into a squared difference. Example 1 ( Sin280°-sin240°)/(cos280°-sin240°)=( )