If $5\tan^2 x - \cos^2 x = 2\cos 2x + 9$, then the value of $\cos 4x$ is (1) $-\dfrac{3}{5}$ (2) $\dfrac{1}{3}$ (3) $\dfrac{2}{9}$ (4) $-\dfrac{7}{9}$
If $5\tan^2 x - \cos^2 x = 2\cos 2x + 9$, then the value of $\cos 4x$ is\\
(1) $-\dfrac{3}{5}$\\
(2) $\dfrac{1}{3}$\\
(3) $\dfrac{2}{9}$\\
(4) $-\dfrac{7}{9}$