Question

I really need some help, please!
Write the equation of a circle with center (3,-9) and radius r=4

Answer 1

equation of a circle formula is (x-h)^2+(y-k)^2=r^2

so just plug in ur x and y values, then since u have your radius...just square it:)

Answer 2

We have a pattern, or formula, if you will, for this type of problem.
If you have a radius r
and a center (h,k)
then the equation of the circle looks like this
\[\Large (x-h)^2 + (y-k)^2 = r^2\]

In your case, h = 3
k = -9

and of course, r = 4

Just plug in and be done :)