若sin(α-π/6)=1/3 则cos(2α-π/3)的值等于

问题描述:

若sin(α-π/6)=1/3 则cos(2α-π/3)的值等于

若sin(α-π/6)=1/3
则cos(2α-π/3)
=cos2(α-π/6)
=1-2sin²(α-π/6)
=1-2×(1/3)²
=1-2/9
=7/9