Prove that: `cos 2theta.cos 2phi+cos^2 (theta+phi) - cos^2 (theta-phi) = cos (2theta + 2phi)`

cos2 theta cos2 phi+sin^(2)(theta-phi)-sin^(2)(theta+phi)=cos(2 theta+2 phi)

prove that (cos3 theta+cos3 phi)/(2cos(theta+phi)-1)=(cos theta+cos phi)cos(theta+phi)-(sin theta+sin phi)sin(theta+phi)

If cos(theta+phi)=m cos(theta-phi) then tan theta is equal to

If "sin" theta+"sin" phi=a and cos theta+cos phi=b find: (i) "sin"(theta+phi) (ii) cos(theta+phi) (iii) cos(theta-phi)

cos 2 (theta+ phi) +4 cos (theta + phi ) sin theta sin phi + 2 sin ^(2) phi=

If 3 tan theta tan phi=1, then (cos (theta-phi))/(cos (theta+phi)) is

3tanthetatanphi=1 , then (cos(theta-phi))/(cos(theta+phi))=?

If 3tan theta tan phi=1 then (cos(theta-phi))/(cos(theta+phi)) is