一、技巧1.变角例1:求证:sin(2α+β)sinα-2cos(α+β)=ssiinnαβ证明:∵2α+β=α+β+α∴sin(2α+β)-2cos(α+β)sinα=sin[(α+β)+α]-2cos(α+β)sinα=sin(α+β)cosα+cos(α+β)sinα-2cos(α+β)sinα=sin(α+β)cosα-cos(α+β)sinα=sin(α+β-α)=sinβ∴sin(2α+β)sinα-2cos(α+β)=ssiinnαβ评析:“角”是三角函数的基本元素,研究三角恒等变换离不开“角”的变换.对单角、倍角、和角、差角等进行适当的变形转化,往往能起到化难为易、化繁为简的作用.(甘肃省通渭县第一中 First, the skills 1. Variation Example 1: Verification: sin (2α + β) sinα-2cos (α + β) = ssiinnαβ Prove: ∵2α + β = α + β + α∴sin (2α + β) -2cos α + β ⁢ sin α = sin α ⁢ β + α α - cos ⁢ 2 cos α + β sin α = sin α + β cos α + cos α + β sin α - (α + β) cosα-cos (α + β) sinα = sin (α + β -α) = sinβ∴ sin (2α + β) sinα- 2cos (α + β) = ssiinnαβ Comment: The basic elements of the trigonometric function, the study of triangular transformation can not be inseparable from the “Angle ” transformation.On the single angle, double angle, angle, angle and other appropriate deformation transformation, often can play the difficult for the easy For the sake of simplicity. (No. 1 in Tongwei County, Gansu Province