411 REFERENCE · Wikibooks
HSC Mathematics Advanced, Extension 1, and Extension 2/3-Unit/Preliminary/Circle geometry
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
A circle is a 2D shape with no sides, corners or vertices.
Arc and Angle
Rule 1: Equal arcs subtend equal angles at the centre of the circle.
Rule 2: Equal angles at the centre of the circle subtends equal arcs.