$\lim_{x \to \frac{\pi}{2}} \dfrac{\cot x - \cos x}{(\pi - 2x)^3}$ equals\\ (1) $\dfrac{1}{24}$\\ (2) $\dfrac{1}{16}$\\ (3) $\dfrac{1}{8}$\\ (4) $\dfrac{1}{4}$