已知cos(30°+α)=根号3/3,则cos(150°-α)等于
问题描述：
已知cos(30°+α)=根号3/3,则cos(150°-α)等于
答
cos(150°-α)=cos[180°-(30°+α)]=-cos(30°+α)=负根号3/3
答
cos(150-a)=cos[180-(30+a)]=-cos(30+a)=负根号3/3
答
cos(150°-α)=cos(180°-30°-α)=cos[180°-(30°+α)]=-cos(30°+α)=-根号3/3
答
因为cos(180-a)=-cosa
所以cos(150-a)=-cos[180-(150-a)]
=-cos(30+a)
=-√3/3
答
cos(30°+α)=√3/3
cos(150°-α)
=cos(180°-(30°+α) )
=-cos(30°+α)
=-√3/3