ρcos2θ=cos(2π /3-θ) ρ(cosθ)^2-(sinθ)^2=cos2π /3*cosθ+sin2π /3*sinθ ρ(cosθ+sinθ)(cosθ+sinθ)=(-1/2)*cosθ+(根号3/2)*sinθ ρ*ρ(cosθ+sinθ)(cosθ+sinθ)=ρ*((-1/2)*cosθ+(根号3/2)*sinθ...