`cos A + cos (240^(@) +A)+ cos (240^(@)-A)=`

cosA+cos(240^(@)+A)+cos(240^(@)-A)=?

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

cos theta + cos (240^(@) + theta ) + cos (240^(@)- theta )=

Prove that cos alpha cos (120^(@) + alpha) cos (240^(@) + alpha) = 1/4 cos 3 alpha

Prove that, cos^(3) alpha + cos^(3) (120^(@) + alpha) + cos^(3) (240^(@) + alpha) = 3/4 cos 3 alpha

I : If x cos theta = y cos (120^@ + theta ) = z cos ( theta + 240^(@)) then xy+ yz+ zx=1 II : cos alpha + cos (120^(@) + alpha ) + cos (120^@ - alpha ) =0

tan 240^@ =

Value of cos 240^@=

If b cos (theta+120^(@))=c cos (theta +240^(@)), then the value of (b+c)/(b-c) tan theta is-