Circle - Equation
The equation for a circle
Unit Circle
The equation of a unit circle - where the center of the circle is located in the origo of the coordinate system and the radius = 1 - can be expressed as
x2 + y2 = 1 (1)
Standard Form
The standard form for the equation of a circle can be expressed as
(x - a)2 + (y - b)2 = r2 (2)
where
a = x coordinate position of the circle center
b = y coordinate position of the circle center
r = circle radius
General Form
The general form for the equation of a circle can be expressed as
x2 + y2 + A x + B y + C = 0 (3)
where
A, B, C = constants
Radius of circle
r = (a2 + b2 - C) 1/2 (4)
Coordinates in the Circle Centre
a = - A / 2 (5a)
b = - B / 2 (5b)