Circle

A circle is a shape consisting of all points in a plane that are at a given distance from a given point, the centre. The distance between any point of the circle and the centre is called the radius.

Circle

The equation of a circle

(xu)2+(yv)2=r2

The equation of a centred circle

x2+y2=r2

Tangency condition of a circle and a line

Tangent to a circle

r2k2+1=k·u-v+n2

where the equation of the tangent line is :

y=kx+n
Keywords: circle, central circle, equation of a circle, tangent to a circle