To find \((fg)(x)\), we need to evaluate \(f(g(x))\).
Given:
- \(f(x) = \sqrt{x - 1}\)
- \(g(x) = 3x - 1\)
Now, we can substitute \(g(x)\) into \(f(x)\):
\[ (fg)(x) = f(g(x)) = f(3x - 1) = \sqrt{(3x - 1) - 1} = \sqrt{3x - 2} \]
Now, let's determine the domain of \((fg)(x)\).
For the function \(f(x)\), \(x - 1\) must be non-negative:
\[ 3x - 2 \geq 0 \ 3x \geq 2 \ x \geq \frac{2}{3} \]
Thus, the domain of \((fg)(x)\) is \(x \geq \frac{2}{3}\).
Among the given responses, none exactly match, but based on your options, "the domain of \((fg)(x)\) is \(x \geq 1\)" is not correct.
As the correct answer is: (fg)(x) = \sqrt{3x - 2} and the domain of (fg)(x) is \(x \geq \frac{2}{3}\).
Please remember there may have been an oversight in the original options you provided since the calculation doesn't lead to any of them being fully correct.