How do you write an equation of a circle with radius of 9 and the center at (-4, 2)?

Aug 3, 2016

${x}^{2} + {y}^{2} + 8 x - 4 y - 61 = 0$

Explanation:

The equation of a circle with radius r and the center at $\left({x}_{0} , {y}_{0}\right)$ is the following:

${\left(x - {x}_{0}\right)}^{2} + {\left(y - {y}_{0}\right)}^{2} = {r}^{2}$

Then, your equation is:

${\left(x + 4\right)}^{2} + {\left(y - 2\right)}^{2} = {9}^{2}$

${x}^{2} + {y}^{2} + 8 x - 4 y + 16 + 4 - 81 = 0$

${x}^{2} + {y}^{2} + 8 x - 4 y - 61 = 0$