Chapter 3 - The Derivative - 3.4 Definition of the Derivative - 3.4 Exercises - Page 176: 3

$x = -2$

The function is undefined when the denominator, $x+2 = 0$, and this can only happen when $x = -2$. Here, there occurs a vertical asymptote, as shown in the graph attached. So $f$ is defined and continuous on $(-\infty,-2)$ and $(-2,\infty)$, therefore it is differentiable on these intervals. At $x=-2$ $f$ is discontinuous, therefore it is not differentiable.