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

If 3tan theta tan phi=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 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

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

If 0 lt theta , phi lt pi and 8 cos theta cos phi cos (theta + phi)+1=0 find theta and phi

If tan theta tan phi=sqrt((a-b)/(a+b)) , prove that a-bcos 2theta)(a-b cos 2phi) is independent of theta and phi .

If theta+phi=alpha and tan theta =k tan phi , prove that: sin alpha=(k+1)/(k-1)"sin"(theta-phi)

If sin theta +sin phi=a and cos theta +cos phi =b then prove cos (theta +phi)=(b^(2)-a^(2))/(b^(2)+a^(2))

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