Sum, Difference, and Multiple-Angle Formulas · Medium problem

$\dfrac{3+4\cos 2x+\cos 4x}{9}$

$\dfrac{3+4\cos 2x+\cos 4x}{8}$

$\dfrac{6+4\cos 2x+\cos 4x}{8}$

$\dfrac{8}{3+4\cos 2x+\cos 4x}$