$$\text { Find the numbers, if any, where the function } f ( x ) = \frac { x - 3 } { x ^ { 2 } - 9 } \text { is discontinuous. }$$

$$\text { Find the numbers, if any, where the function } f ( x ) = \frac { x - 3 } { x ^ { 2 } - 9 } \text { is discontinuous. }$$