# Equation of Circle

• Oct 15th 2009, 02:20 PM
sunnyyueliang
Equation of Circle
I need help figuring out an equation. The equation of a circle with the center of the circle at the origin (0,0) on the Cartesian grid is: x^2+y^2=r^2.
But what is the equation of the center of the circle is not at the origin?
• Oct 15th 2009, 02:23 PM
e^(i*pi)
Quote:

Originally Posted by sunnyyueliang
I need help figuring out an equation. The equation of a circle with the center of the circle at the origin (0,0) on the Cartesian grid is: x^2+y^2=r^2.
But what is the equation of the center of the circle is not at the origin?

For a circle with centre $(a,b)$ the equation is

$(x-a)^2 + (y-b)^2 = r^2$
• Oct 15th 2009, 06:29 PM
pacman
with center @ (h,k), it is (x - h)^2 + (y - k)^2 = (r)^2

examples:

i) (x - 2)^2 + (y - 3)^2 = 25

ii) (x + 2)^2 + (y + 3)^2 = 9

see graphs