(a) To find the probabilities, we use \(P(X = x) = k(x^2 - 1)\) for each value of \(x\):
- For \(x = -2\), \(P(X = -2) = k((-2)^2 - 1) = 3k\).
- For \(x = 2\), \(P(X = 2) = k(2^2 - 1) = 3k\).
- For \(x = 3\), \(P(X = 3) = k(3^2 - 1) = 8k\).
Since the total probability must be 1, we have:
\(3k + 3k + 8k = 1\)
\(14k = 1\)
\(k = \frac{1}{14}\)
Thus, the probability distribution table is:
| \(x\) | -2 | 2 | 3 |
|---|
| \(P(x)\) | \(\frac{3}{14}\) | \(\frac{3}{14}\) | \(\frac{8}{14}\) |
(b) To find \(E(X)\), we calculate:
\(E(X) = (-2) \times \frac{3}{14} + 2 \times \frac{3}{14} + 3 \times \frac{8}{14}\)
\(= \frac{-6}{14} + \frac{6}{14} + \frac{24}{14}\)
\(= \frac{12}{14} = \frac{12}{7}\)
To find \(\text{Var}(X)\), we use:
\(\text{Var}(X) = (-2)^2 \times \frac{3}{14} + 2^2 \times \frac{3}{14} + 3^2 \times \frac{8}{14} - (E(X))^2\)
\(= 4 \times \frac{3}{14} + 4 \times \frac{3}{14} + 9 \times \frac{8}{14} - \left(\frac{12}{7}\right)^2\)
\(= \frac{12 + 12 + 72}{14} - \frac{144}{49}\)
\(= \frac{96}{14} - \frac{144}{49}\)
\(= \frac{192}{49}\)