sin(pai/6-a)=1/4,则sin(pai/6+2a)=
问题描述：
sin(pai/6-a)=1/4,则sin(pai/6+2a)=
答
cos(π/3-2a)
=cos[2(π/6-a)]
=1-2sin²(π/6-a)]
=1-2(1/4)²
=7/8
sin(π/6+2a)
=cos[π/2-(π/6+2a)]
=cos(π/3-2a)
=7/8