若cos(π/6+α)=√2/4,则cos(5π/6-α)的值为( )
问题描述：
若cos(π/6+α)=√2/4,则cos(5π/6-α)的值为( )
答
cos(5π/6-α)
=cos[π-(π/6+α)]
=-cos(π/6+α)=√2/4