Suppose that $X$ describes the random variable that can take on only three values, $X = (1,2,3)$. The probability density function is:

$$f(x) = \left\{ \begin{array}{ll} \frac{x^2}{14}, & x \in X \\\ 0, & \text{otherwise} \end{array} \right. $$

Which of the following is **TRUE**?