Answer
The domain is the set of real numbers greater than or equal to $0$.
Work Step by Step
The given function is
$y=\sqrt{4x}$
The radicand cannot be negative.
So, $4x$ is greater than or equal to zero.
$\Rightarrow 4x\geq 0$
Divide each side by $4$.
$\Rightarrow x\geq 0$
Hence, the domain is the set of real numbers greater than or equal to $0$.
