cos(π/6-α)=m,m绝对值小于等于1,求cos(5π/6+α)
问题描述：
cos(π/6-α)=m,m绝对值小于等于1,求cos(5π/6+α)
答
cos(5π/6+α)=-cos[π-（5π/6+α)]=-cos(π/6-α)
所以cos(5π/6+α)=-m