1. Chapter 25 Circle Properties

2. Circles Circumference = Distance whole way round Arc = Distance round part of circle Radius = Line from centre to edge Diameter = Line from edge to edge through the centre

3. Chord = Line from edge to edge not through the centre Tangent = Line outside circle that touches it once Sector = Slice of circle Segment = Part of Circle

4. Angles in Circle Angle in a semi-circle = 90 o Angle at centre = twice angle at edge (if starting & finishing at same place) Angles at edge are equal (if starting & finishing at same place) Opposite angles in a cyclic quadrilateral add to 180 o

5. Tangents The angle between the radius and the tangent is always 90 o