Answer
Standard Form: $x^2+y^2=9$
General Form. $x^2+y^2-9=0$
Refer to the graph below.
Work Step by Step
The standard form of acircle's equation is $(x-h)^2+(y-k)^2=r^2$ where $r$=radius and $(h, k)$ is the center.
Substitute $3$ to $r$ and $0$ to both $h$ and $k$ in the standard form above to obtain:
\begin{align*}
(x-0)^2+(y-0)^2&=3^2\\
x^2+y^2&=9
\end{align*}
General form of the equation of a circle is $x^2+y^2 + ax+by+c=0$.
Subtract $9$ from each side of the equation above to obtain:
\begin{align*}
x^2+y^2-9&=9-9\\
x^2+y^2-9&=0
\end{align*}
With $r=3$ and center at $(0, 0)$, plot the points $3$ units directly above, below, to the left, and to the right of the circle$. Then, connect these four points using a smooth curve to form a circle.
Refer to the graph above.
