Write the equation of a circle centered at the origin with radius 9.

Answer 1

Center Radius form of a circle (x-h)^2 + (y-k)^2 = r^2, where the center is (h,k) and r represents the radius

(x - 0)^2 +(y -k)^2 = 9^2

x^2 + y^2 = 81

Answer 2

The general equation of a circle is:

(x-h)^2 + (y-k)^2 = r^2

Where h and k give you the coordinates of the center of the circle, h being the x coordinate and k being the y coordinate

r gives you the radius of the circle

Since the origin is at (0,0), we know that h and k are both 0. Since the give us the radius, we also know that r=9

So, with everythinhg together, we have something like this:

(x-0)^2 + (y-0)^2=9^2

Which can be simplified to

x^2 + y^2 = 81

Good luck!