\( \Large 2 \cos x - \cos 3x - \cos 5x = 2 \cos x - 2 \cos x \cos 4x \)

= \( \Large 2 \cos x \left(1- \cos 4x\right) = 2 \cos x 2 \sin^{2} 2x \)

= \( \Large 4 \cos x \left(2 \sin x \cos\ x\right)^{2} = 16 \sin^{2}x \cos^{3}x \)