How do you write an equation in standard form of a circle?

(x - h)2 + (y - k)2 = r2

where h is the x coordinate of the center of the circle.

where k is the y coordinate of the center of the circle.

where x is the x coordinate of point (x,y) on the edge of the circle.

where y is the y coordinate of point (x,y) on the edge of the circle.

Additional assistance here:

http://www.mathwarehouse.com/geometry/circle/equation-of-a-circle.php