`piltalpha-betalt3pi`,`sinalpha+sinbeta=-21/65`,`cosalpha+cosbeta="-27/65`,then `cos((alpha-beta)/2)=` (A) `-6/65` (B) `-3/sqrt(130)` (C) `3/sqrt(130)` (D) `6/65`

pi

Le alpha and beta be such that pi

If cosalpha=3/5 and cosbeta=5/13 then cos^2((alpha+beta)/2)=16/65

Let alpha, beta be such that pi lt alph-betalt3piif sin alpha+sinbeta=-21/65and cos alpha+cos beta =-27/65, then the value of cos""(alpha-beta)/(2), is

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

If sinalpha+cosbeta=5/4 and cosalpha+sinbeta=3/4 , then value of sin(alpha+beta)=?

Let alphaandbeta be such that piltalpha-betalt3pi . If sinalpha+sinbeta=-(21)/(65)and cosalpha+cosbeta=-(27)/(65) , then the value of "cos"((alpha-beta))/(2) is

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

Let alpha, beta be such that pi lt alpha -beta lt 3 pi. If sin alpha + sin beta =- (21)/(65) and cos alpha + cos beta =- (27)/(65) and if the value of cos "" (alpha - beta)/(2) =(-a)/(sqrtb), then a xx b=