Question

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 \( k - 2 = \) 
 

• A. 2
• B. 1
• C. 0
• D. 3

Hint:

For piecewise functions, check the left-hand and right-hand derivatives at the boundary points to determine non-differentiability.