One of the fundamental shapes in geometry. The unit circle can be described by the equation x2+y2=1; in other words, every pair of real numbers (x,y) which satisfy this equation corresponds to a point (x,y) on the edge of the unit circle. When speaking of circles, it is common to mention only the radius, since every circle has symmetry to a high degree. Below, I use R to denote the radius of the circle. R=24chars.
AV R VA
The above circle was formed using the pythagorean triple (5,12,13), i.e. the points (5/13,12/13), (12/13,5/13), (-5/13,12/13), (-12/13,5/13), (5/13,-12/13), (12/13,-5/13), (-5/13,-12/13) and (-12/13,-5/13).
Some properties of any circle of radius R centered on the origin:
x2+y2=R2 is the generating equation; letting x=R*cos(t) and y=R*sin(t) for angles t will also generate the circle (all points (x,y) on the edge of said circle).