If `2cosx+2cos3x=cosy` and `2sinx+2sin3x=siny` then `cos2x=`

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 cosx+cosy+cosalpha=0 and sinx+siny+sinalpha=0 then cot((x+y)/2)= ................. A) sin alpha B) cos alpha C) cot alpha D) sin ((x+y)/(2))

If cosx+cosy+cosz=sinx+siny+sinz=0" then "cos(x-y)=

If cosx+cosy+cosz=sinx+siny+sinz=0" then "cos(x-y)=

cosx + sinx = cos2x + sin2x

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