题目

若sin(α＋π/6)=1/3,则cos(2π/3－2α)的值为

提问时间：2020-10-11

答案

cos(2π/3-2α)
=-cos[π-(2π/3-2α)]
=-cos(π/3+2α)
=-cos[2(π/6+α)]
=-{1-2[sin(π/6+α)]^2}
=-(1-2/9)
=-7/9