CIRCLES

• Arc


  a smooth curve joining two endpoints.
• Circle

  A round plane figure whose boundary consists of points equidistant from a fixed point.
• Centre

  the fixed point from which all points on the boundary of the circle are equidistant.
• Radius

  The distance from the centre of a circle to the outside.

  The radius of the circle is half the diameter of the circle.

  The plural of radius is radii.
• Diameter

  The distance across the circle going through the centre.
• Circumference

  The distance once around the circle.
• Arc

  A part of the circumference.
• Major arc – A major arc is greater than half the circumference.
• Minor arc – A minor arc is less than half the circumference.
• Chord

  A line segment going from one point of the circumference to another but does not go through the centre.
• Secant

  A line that goes through the circle at two points.
• Tangent

  A straight line that touches the circle at a single point only.
• Sector

  A section of the circle created by two radii.
• Major sector – A major sector has a central angle which is more than 180
• Minor sector – A minor sector has a central angle which is less than 180
• Semi circle

  Half of a circle. Could be considered a sector where the circle has be split by the diameter.
• Quadrant

  A quarter of a circle, created by two perpendicular radii.
• Segment

  A section of the circle created by a chord.
• Major segment – a segment where the arc is greater than half the circumference.
• Minor segment – a segment where the arc is less than half the circumference.
• An inscribed angle in a circle is formed by two chords that have a common end point on the circle.
• An inscribed angle in a circle is formed by two chords that have a common end point on the circle.