已知sin(α-15°)=1/3,则cos(30°-2α)的值为多少?

问题描述:

已知sin(α-15°)=1/3,则cos(30°-2α)的值为多少?

cos(30°-2a)=1-2[sin(a-15°)]^2
=1-2/3
=1/3