Si $y = \frac{x^4 - x^2 + 1}{x^2 + \sqrt{3}x + 1}$ y $\frac{dy}{dx} = ax + b$, entonces el valor de $a - b$ es:
$$ \begin{array}{llll} \text{a. } \cot \frac{\pi}{8} & \text{b. } \cot \frac{\pi}{12} & \text{c. } \tan \frac{5\pi}{12} & \text{d. } \tan \frac{5\pi}{8} \end{array} $$