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

Feb 21, 2016

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

#### Explanation:

The standard form of the equation of a circle is

${\left(x - a\right)}^{2} + {\left(y - b\right)}^{2} = {r}^{2}$

where (a , b ) are the coords of centre and r , the radius

here (a , b ) = (7 , -3 ) and r = 9. Substituting into standard equation gives

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