已知sin(π/3-a)=1/3,则cos(π/3+2a)=

问题描述:

已知sin(π/3-a)=1/3,则cos(π/3+2a)=

cos(π/3+2a)=-cos(2π/3-2a)=-cos[2(π/3-a)]=-[1-2sin²(π/3-a)]=-[1-2/9]=-7/9