If `3tanthetatanphi=1` , then prove that `2cos(theta+phi) + cos(theta-phi)=0`

If 3 tan theta tan phi=1 , then prove that 2 cos (theta+varphi)=cos (theta-varphi) .

If 3tan theta tan phi=1. Prove that 2cos(theta+phi)=cos(theta-phi)

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

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

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

If 3tantheta.tanphi=1 . evalute: (cos(theta-phi))/(cos(theta+phi)).

If tan^(2)theta=2tan^(2)phi+1, prove that cos2 theta+sin^(2)phi=0

If phi be the exterior angle of a regular polygon of n sides and theta is any constant, then prove that costheta+cos(theta+phi)+cos(theta+2phi)+…+to n term =0

If tan^(2)theta=1+2tan^(2)phi, prove that cos2 phi=1+2cos2 theta

The sides of triangle are in A.P. and the greatet and least angle are theta and phi: prove that 4(1-cos theta)(1-cos phi)=cos theta+cos phi