cos^2A+cos^2(2π/3+A)+cos^2(4π/3+A)
问题描述:
cos^2A+cos^2(2π/3+A)+cos^2(4π/3+A)
答
cos^2A+cos^2(2π/3+A)+cos^2(4π/3+A)=COS^2A+(-COS(-π/3+A))(-COS(-π/3+A))+(-COS(π/3+A))(-COS(π/3+A))=COS^2A+COS^2(-π/3+A)+COS^2(π/3+A)=1/2(1+COS2A)+1/2{(1+COS[-2π/3+2A])}+1/2{(1+COS[2π/3+2A])}=...