Once you know $x=0$ at the y-intercept, substitute $x=0$ into $y=\sqrt{x+9}$.

After substituting $x=0$, you will get $y=\sqrt{9}$. Remember that the square root symbol $\sqrt{\phantom{x}}$ refers to the nonnegative (principal) square root.

In Desmos, type y = sqrt(x + 9) to graph the function $y=\sqrt{x+9}$.

Either:

• Click on the graph where it crosses the y-axis (where $x=0$), or
• Add a table for the function and include $x=0$ as an entry.

Read off the corresponding y-value; that is the y-coordinate of the y-intercept.

The y-intercept is the point where the graph crosses the y-axis. On the y-axis, the $x$-coordinate is $0$. So to find the y-intercept of $y=\sqrt{x+9}$, we set $x=0$.

Plug $x=0$ into the equation:

$y = \sqrt{x + 9}$ becomes $y = \sqrt{0 + 9}$.

So $y = \sqrt{9}$.

Now simplify $\sqrt{9}$. The principal (nonnegative) square root of $9$ is $3$.

So the y-intercept is $(0, 3)$, and the value of $y$ is 3.