If `cosalpha+cosbeta=a, sinalpha+sinbeta=b,` then `cos(alpha+beta)` is equal to (A) `(2ab)/(a^2+b^2)` (B) `(a^2+b^2)/(a^2-b^2)` (C) `(a^2-b^2)/(a^2+b^2)` (D) `(b^2-a^2)/(b^2+a^2)`

If cosalpha+cosbeta=a ,sinalpha+sinbeta=b and alpha-beta=2theta, then (cos3theta)/(costheta)=

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

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

If tantheta=a/b , then (asintheta+bcostheta)/(asintheta-bcostheta) is equal to (a) (a^2+b^2)/(a^2-b^2) (b) (a^2-b^2)/(a^2+b^2) (c) (a+b)/(a-b) (d) (a-b)/(a+b)

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

If acos alpha+b sin beta=c , a sin alpha+b cos beta=c then sin(alpha+beta) (2c^(2)+a^(2)+b^(2))/(ab) (2c^(2)-a^(2)-b^(2))/(ab) (2c^(2)+a^(2)-b^(2))/(2ab) (2c^(2)-a^(2)-b^(2))/(2ab)

If sinalpha+sinbeta=a and cosalpha+cosbeta=b , prove that tan(alpha-beta)/2=+-sqrt((4-a^2-b^2)/(a^2+b^2)) .

If sinalpha+sinbeta=a and cosalpha+cosbeta=b , prove that tan((alpha-beta)/2)=+-sqrt((4-a^2-b^2)/(a^2+b^2)) .

If sinalpha+sinbeta=a and cosalpha+cosbeta=b , prove that tan((alpha-beta)/2)=+-sqrt((4-a^2-b^2)/(a^2+b^2)) .

If sinalpha+sinbeta=a and cosalpha+cosbeta=b , prove that tan((alpha-beta)/2)=+-sqrt((4-a^2-b^2)/(a^2+b^2)) .