# The center of a circle is at (7, -3) and it has a radius of 9. What is the equation of the circle?

Apr 9, 2018

${\left(x - 7\right)}^{2} + {\left(y + 3\right)}^{2} = 81$

#### Explanation:

$\text{the equation of a circle in standard form is}$

$\textcolor{red}{\overline{\underline{| \textcolor{w h i t e}{\frac{2}{2}} \textcolor{b l a c k}{{\left(x - a\right)}^{2} + {\left(y - b\right)}^{2} = {r}^{2}} \textcolor{w h i t e}{\frac{2}{2}} |}}}$

$\text{where "(a,b)" are the coordinates of the centre and r is}$
$\text{the radius}$

$\text{here "(a,b)=(7,-3)" and } r = 9$

${\left(x - 7\right)}^{2} + {\left(y - \left(- 3\right)\right)}^{2} = {9}^{2}$

$\Rightarrow {\left(x - 7\right)}^{2} + {\left(y + 3\right)}^{2} = 81 \leftarrow \textcolor{red}{\text{equation of circle}}$