Chapter 9: Circles

Circle Properties

Circles

Key Terms

TermDefinition
RadiusDistance from center to circle
DiameterChord through center = 2r2r
ChordLine segment with endpoints on circle
ArcPart of circle between two points

Chord Properties

  1. Equal chords are equidistant from center
  2. Perpendicular from center bisects chord

Angle Properties

  • Angle at center = 2 × Angle at circumference
  • Angles in same segment are equal
  • Angle in semicircle = 90°90°
  • Cyclic Quadrilateral: Opposite angles sum to 180°180°