cos(2π/3+2α)=-cos[π-(2π/3+2α)]=-cos(π/3-2α)=-cos[2(π/6-α)]=-{1-2[sin(π/6-α)]^2}=-(1-2/9)=-7/9希望我的回答对你有帮助，采纳吧O(∩_∩)O！
