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)

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