化简cos²B+cos²(2π/3-B)

问题描述:

化简cos²B+cos²(2π/3-B)

原式=(1 +cos 2B) /2 +[ 1 +cos (4π/3 -2B) ] /2=1 +(1/2) cos 2B +(1/2) cos (4π/3 -2B)=1 +(1/2) cos 2B +(1/2) (cos 4π/3 cos 2B +sin 4π/3 sin 2B)=1 +(1/2) cos...