The number of solutions of the equation \( \cos 2\theta \cos \dfrac{\theta}{2}+\cos \dfrac{5\theta}{2}=2\cos^{3}\dfrac{5\theta}{2} \) in \( \left[ -\dfrac{\pi}{2},\dfrac{\pi}{2} \right] \) is:
\(9\)
\(7\)
\(6\)
\(5\)