三角函数之求值问题sin(pai/6-α)=1/3则cos(2pai/3+2α)= (pai为圆周率）_数学解答

三角函数之求值问题
sin(pai/6-α)=1/3则cos(2pai/3+2α)= (pai为圆周率）

人气：365 ℃　时间：2020-08-19 18:12:55

解答

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