cos^2a+cos^2b-cos(a+b)cos(a-b)

я исправил,удалите фото

cos^2a+cos^2b-cos (a+b)cos (a-b)=cos^2a+cos^2b-1/2[cos (a+b-a+b)+cos (a+b+a-b)]=cos^2a+cos^2b-(1/2)cos2b-(1/2)cos2a=(1+cos2a)/2+(1+cos2b)/2-(1/2)cos2b-(1/2)cos2a=1/2+(1/2)cos2a+1/2+(1/2)cos2b-(1/2)cos2b-(1/2)cos2a=1