三角函数诱导公式已知sin(π+α)= -1/2,计算1.sin(5π-α)2.sin(π/2+α)3.cos(α- 3

sin(π+α)= -1/2
-sinα= -1/2
sinα= 1/2
1.sin(5π-α)=sin(π-α)=sinα=1/2
2.sin(π/2+α)=sin( π- π/2-α)=sin( π/2-α)=cosα=√(1-sin²a)=√3/2
3.cos(α- 3π/2)=cos(α- 3π/2+2π)=cos(α+π/2)=cos(π/2-α)=sinα= 1/2
4.tan(π/2-α)=sin(π/2-α)/cos(π/2-α)=cosa/sina=(√3/2)/(1/2)=√3