终站狂猛
幼苗
共回答了90个问题 举报
原式=cos2θ+(cosθcos2π/3-sinθsin2π/3)2+(cosθcos2π/3+sinθsin2π/3)2
=cos2θ+(-1/2*cosθ-√3/2*sinθ)2+(-1/2*cosθ+√3/2*sinθ)2
=cos2θ+1/4*cos2θ+√3/2*sinθcosθ+3/4*sin2θ+1/4*cos2θ-√3/2*sinθcosθ+3/4*sin2θ
=3/2*cos2θ+3/2*sin2θ
=3/2*(cos2θ+sin2θ)
=3/2
1年前
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