If `cosalpha+cosbeta=0=sinalpha+sinbeta`, then prove that `cos2alpha +cos2beta=-2cos(alpha +beta)`.

If cos alpha+cos beta=0=sin alpha+sin beta, then prove that cos2 alpha+cos2 beta=-2cos(alpha+beta)

If cos alpha+cos beta=0=sin alpha+sin beta, then prove that cos2 alpha+cos2 beta=-2cos(alpha+beta)

If cos alpha+cos beta=0=sin alpha+sin beta. Prove that cos2 alpha+cos2 beta=-2cos(alpha+beta)

If cosalpha+cosbeta=0=sinalpha+sinbeta , then cos2alpha+cos2beta=?

If cos alpha+cos beta=0=sin alpha+sinbeta, then cos2alpha+cos 2beta=

If cos alpha+cos beta=0=sin alpha+sin beta then cos2 alpha+cos2 beta=

If cosalpha+cosbeta=0=sinalpha+sinbeta+siny, prove that (i) sumcos3alpha=3cos(alpha+beta+gamma) 2. sumsin3alpha=3sin(alpha+beta+gamma) 3. sumcos^2alpha=sumsin^2alpha=3/2

If cos alpha + cos beta = 0 = sin alpha + sin beta, then value of cos 2 alpha + cos 2 beta is

If cos alpha+cos beta=0=sin alpha+sin beta, then cos2 alpha+cos2 beta is equal to