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