Graph of the Square Root Function $y = \sqrt{x}$

$y = \sqrt{x}$ is the non-negative number whose square is $x$, so its domain is $x \geq 0$ and its range is $y \geq 0$.

It is the inverse of $y = x^2$ (for $x \geq 0$): starting at the origin, it rises ever more gently. Because it contains a radical it is called an irrational function, and it is not real for negative $x$.