数学三角函数化简题
问题描述：
数学三角函数化简题
18.化简sin(π-α)sin([π/2]-α)/cos(π+α)cos([π/2]+α);
(2)若tanα=2求 [sinα+cosα]/[（sinα-cosα）+cos^2α]之值
19.已知tan(α+β)=3,tan(α-β)=5,求tan2α,tan2β的值
答
18.诱导公式：sin(π-α)=sinα； sin([π/2]-α ) =cosα cos(π+α)=-cosα; cos([π/2]+α)=-sinα∴ sin(π-α)sin([π/2]-α)/cos(π+α)cos([π/2]+α)=(sinαcosα)/[(-cosα)(-sinα)=(sinαcosα)/(sinαco...