#### Answer

$[0,∞)$

#### Work Step by Step

The function $f(x)=\sqrt x$ is the square root function. We can take the square root of any non-negative number $x$, because we can find a number $a$ such that $a^{2}=x$.
For example, $\sqrt 0=0$, because $0^{2}=0$. Also, $\sqrt 9=3$, because $3^{2}=9$
We cannot take the square root of a negative number, because there is no number that can be multiplied by itself to produce a negative number.
Therefore, we can take the square root of any number greater than or equal to 0.