If `tan^2 theta = 1+2 tan^2 phi`, prove that `cos 2 phi = 1 + 2 cos 2 theta`.
Channel: Doubtnut
Date: 2020-04-05

If `tan^2 theta = 1+2 tan^2 phi`, prove that `cos 2 phi = 1 + 2 cos 2 theta`.