If $5\left( {{{\tan }^2}x - {{\cos }^2}x} \right) = 2\cos 2x + 9$, then the value of $\cos 4x$ is :

Question

If $5\left( {{{\tan }^2}x - {{\cos }^2}x} \right) = 2\cos 2x + 9$,

then the value of $\cos 4x$ is :

${1 \over 3}$

${2 \over 9}$

$ - {7 \over 9}$

$ - {3 \over 5}$

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