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=0=sinalpha+sinbeta , then cos2alpha+cos2beta=?

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 sin alpha+sin beta=a and cos alpha+cos beta=b prove that :cos(alpha-beta)=(1)/(2)(a^(2)+b^(2)-2)

If sinalpha+sinbeta=a and coslapha+cosbeta=b then prove that sin(alpha+beta)=(2ab)/(a^2+b^2)

If s in alpha+s in beta=a and cos alpha+cos beta=b show that :cos(alpha+beta)=(b^(2)-a^(2))/(b^(2)+a^(2))

If tan theta=(a)/(b), then (a sin theta+b cos theta)/(a sin theta-b cos theta) is equal to (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 s in alpha+s in beta=a and cos alpha+cos beta=b prove that: cos(alpha-beta=(a^(2)+b^(2)-2)/(2))

If s in alpha+s in beta=a and cos alpha+cos beta=b show that: sin(alpha+beta)=(2ab)/(a^(2)+b^(2))cos(alpha+beta)=(b^(2)-a^(2))/(b^(2)+a^(2))