问题描述： cosθ^2+cos(θ+2π/3)^2+cos(θ-2π/3)^2 计算 1个回答 分类：数学 2014-10-01 问题解答： 我来补答 cos^2θ+cos^2(θ+2π/3)+cos^2(θ-2π/3)=(1+cos2θ)/2+[1+cos(2θ+4π/3)]/2+[1+cos(2θ-4π/3)]/2=3/2 +[cos2θ+cos(2θ+4π/3)+cos(2θ-4π/3)]/2cos2θ+cos(2θ+4π/3)+cos(2θ-4π/3)=cos2θ+cos2θcos(4π/3)-sin2θsin(4π/3)+cos2θcos(4π/3)+sin2θsin(4π/3)=cos2θ+2cos2θcos(4π/3)=0所以 原式=3/2 展开全文阅读
