Define \[ f(x) = \begin{cases} b - ax, & \text{if } x < 2 \\ 3, & \text{if } x = 2 \\ a + 2bx, & \text{if } x > 2 \end{cases} \]
If \( \lim_{x \to 2} f(x) \) exists, then find \( \frac{a}{b} \).
If \( f(x) \) is defined as follows:
$$ f(x) = \begin{cases} 4, & \text{if } -\infty < x < -\sqrt{5}, \\ x^2 - 1, & \text{if } -\sqrt{5} \leq x \leq \sqrt{5}, \\ 4, & \text{if } \sqrt{5} \leq x < \infty. \end{cases} $$ If \( k \) is the number of points where \( f(x) \) is not differentiable, then \( k - 2 = \)