For What Value of the Constant $c$ Is the Function $f$ Continuous On

Short Answer

For what value of the constant $c$ is the function $f$ continuous on $( - \infty , \infty )$ ?
$$f ( x ) = \left\{ \begin{array} { l l l } c x + 5 & \text { for } & x \leq 2 \\c x ^ { 2 } - 5 & \text { for } & x > 2\end{array} \right.$$