If `2 cosx + 2 cos3x = cosy` and `2 sinx +2 sin3x=siny` then `cos 2x=`

If 2cosx+2cos3x=cosy and 2sinx+2sin3x=siny then cos 2x=

If 3cosx + 2cos3x=cosy , 3sinx + 2sin3x =siny , then cos2x equals

If cosx + cosy + cosz = 0 and sinx + siny + sinz =0 , then show that cos (x-y) + cos(y - z) + cos(z - x) = - 3/2.

If cosx + cosy + cosz = 0 "and" sinx + siny + sinz =0, "then show that" cos (x-y) + cos(y - z) + cos(z - x) = - 3/2.

If sinx siny = 3 (cosy - cos x) then (sin3x)/(sin3y) =

if x and y are acute angles such that cosx + cosy = 3/2 and sinx + siny = 3/4 then sin(x+y)=

if x and y are acute angles such that cosx + cosy = 3/2 and sinx + siny = 3/4 then sin(x+y)=

If cosx+cosy+cosz=0 and sinx+siny+sinz=0 then show that cos(x-y)+cos(y-z)+cos(z-x)=-3/2

If cos x. cosy+sinx.siny=-1 then cosx+cosy is :