After you substitute $x=0$, compute $0^2$ and then simplify $49 - 0^2$ before taking the square root.

What is the nonnegative number whose square is $49$? Remember that the square root symbol $\sqrt{a}$ refers to the nonnegative root.

In Desmos, type p(x) = sqrt(49 - x^2) so the graph of the function is displayed.

Either (a) add a table for p(x) and enter 0 in the x-column, or (b) type a separate expression sqrt(49 - 0^2). Desmos will show the numerical value of this expression; that is the value of $p(0)$.

We are given $p(x)=\sqrt{49 - x^2}$.

To find $p(0)$, replace $x$ with $0$:

First compute $0^2$ and then subtract:

• $0^2 = 0$
• $49 - 0 = 49$

So we have

The symbol $\sqrt{\phantom{x}}$ means the principal (nonnegative) square root. The nonnegative number whose square is $49$ is $7$.

Therefore,