упростите 2 cos 10°cos40° - cos50°

cos10cos40=1/2(cos(10-40)+cos(10+40))=1/2(cos(-30)+cos50)=*cos(-30)=cos(30) -четная*=1/2(cos30+cos50)2*1/2(cos30+cos50)-cos50==cos30+cos50-cos50=cos30=sqrt(3)/2