Study notes

Circle Properties

Angle properties of circles: semicircle, centre vs circumference, same segment, cyclic quadrilaterals, and tangents.

What this topic covers

  • The angle in a semicircle is 90 degrees
  • The angle at the centre is twice the angle at the circumference, on the same arc
  • Angles in the same segment are equal
  • Opposite angles of a cyclic quadrilateral sum to 180 degrees
  • A tangent is perpendicular to the radius at the point of contact
  • Two tangents from the same external point are equal in length

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