Answer
$x\geq3$
Work Step by Step
The expression under the square root must be non-negative, thus $x^3-3x^2=x^2(x-3)\geq0$
We know that $(x-k)^2\geq0$ for all $k$.
So here for the inequality to be true, $x-3\geq0\\x\geq3$
So the domain is $x\geq3$
