The standard equation of a circle: In the plane rectangular coordinate system, the standard equation of a circle with a radius of R and a center of point O(a, b) is (x-a) 2+(y-b) 2 = r 2.

General equation of the circle: expand the standard equation of the circle, shift the terms, and merge the similar terms, and the general equation of the circle can be obtained as X 2+Y 2+DX+EY+F = 0. Compared with the standard equation, in fact, D=-2a, E=-2b and f = a 2+b 2-r 2.