To find \((f \circ g)(x)\), we need to evaluate \(f(g(x))\).
Given the functions:
- \(f(x) = \sqrt{x - 1}\)
- \(g(x) = 3x - 1\)
Now we compute \(f(g(x))\):
\[ f(g(x)) = f(3x - 1) = \sqrt{(3x - 1) - 1} = \sqrt{3x - 2} \]
So we have:
\[ (f \circ g)(x) = \sqrt{3x - 2} \]
Next, we need to determine the domain of \((f \circ g)(x)\).
The expression \(\sqrt{3x - 2}\) is defined when:
\[ 3x - 2 \geq 0 \]
Solving this inequality:
\[ 3x \geq 2 \ x \geq \frac{2}{3} \]
Thus, the domain of \((f \circ g)(x)\) is \(x \geq \frac{2}{3}\).
Summarizing:
\[ (f \circ g)(x) = \sqrt{3x - 2} \quad \text{and the domain is } x \geq \frac{2}{3}. \]
Given the options provided, none of them match the correct answer exactly. If you are looking for a precise match in an answer sheet, please check for \( \sqrt{3x - 2} \) with domain \( x \geq \frac{2}{3} \).