" 1.3."cos A+cos(120^(@)-A)+cos(120^(@)+A)=0

cosA+cos(120^(@)-A)+cos(120^(@)+A)=0

cosA+cos(120^(@)-A)+cos(120^(@)+A)=0

cos120^(@)=

Prove the following: (i) "sin" alpha+"sin"(alpha+(2pi)/(3))+"sin"(alpha+(4pi)/(3))=0 (ii) cos A+cos(120^(@)-A)+cos(120^(@)+A)=0 .

Prove that (i) sin A+sin (120^(@)+A)+sin(240^(@)+A)=0 (ii) cos A+cos (120^(@)+A)+cos (120^(@)-A)=0

Prove the following : cos A + cos (120^@ - A) + cos (120^@+ A) = 0 .

" cos x + cos " (120^(@) -x ) + " cos "(120^(@) +x)=0

cos (120^(@)) is -

Prove that : cos^(2)A+cos^(2)(A+pi/3)+cos^(2)(A-pi/3) =1/2[2cos^(2)A+2cos^(2)(A+60^(@))+2cos^(2)(A-60^(@))] =1/2[1+cos2A+1+cos(2A+120^(@))+1+cos(2A-120^(@))] 1/2[3+cos2A+cos(2A+120^(@))+cos(2A-120^(@))] 1/2[3+cos2A+2cos(2A+120^(@)+2A-120^(@))/(2).cos(2A+120^(@)-2A+120^(@))/(2)] =1/2[3+cos2A+2cos2Acos120^(@)] =1/2[3cos2A+2cos2Acos(90^(@)+30^(@))] =1/2[3+cos2A-2.cos2A.(1/2)] =1/2(3+cos2A-cos2A) =3/2 = RHS Hence Proved.

cos A + cos ( 120 ^@+A ) + cos ( 120^@ -A ) is