Question

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

Answer 1

`x^2+y^2+8x-4y-61=0`

Explanation:

The equation of a circle with radius r and the center at `(x_0,y_0)` is the following:

`(x-x_0)^2+(y-y_0)^2=r^2`

Then, your equation is:

`(x+4)^2+(y-2)^2=9^2`

`x^2+y^2+8x-4y+16+4-81=0`

`x^2+y^2+8x-4y-61=0`