Question

高中数学三角函数，详细一点解答拜托了。

Answer 1

α是第四象限角，又tan(π/3+α)=-5/12<0，因此π/3+α是第四象限角
sin(π/3+α)<0
cos(π/6 -α)
=sin[π/2-(π/6-α)]
=sin(π/3+α)
=-5/√(5²+12²)
=-5/13
选D

Answer 2

3π/2<α<2π
tan(π/3+α)<-5/12
3π/2<α<5π/3
sin(π/3+α)=-5/13
cos(π/6-α)=sin[π/2-(π/6-α)]=sin(π/3+α)=-5/13
选D