Cyclic Quadrilaterals

Identify a cyclic quadrilateral and state that opposite interior angles sum to 180 degrees, using this to find one missing angle.

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Learning objective overview

Master Teaching Guide coverage for this objective.

Current NZC (2007)
  • GM6-4
New NZC (2026)
  • NZC26-P4-GEO-SHP-P-Y9-01

Resources

Terminology

  • Cyclic quadrilateral
  • Opposite angles
  • Circumscribed circle
  • Exterior angle
  • Interior angle
  • Supplementary angles

Task goals

  • Identify a cyclic quadrilateral as a four-sided shape with every vertex on a circle.
  • State and apply the cyclic quadrilateral theorem (opposite interior angles sum to 180 degrees) to find one missing angle.
  • Apply the exterior-angle property of a cyclic quadrilateral (an exterior angle equals the interior opposite angle) to find a missing angle.
  • Set up and solve an algebraic equation from two opposite angles given as expressions to find an unknown variable.
  • Combine the cyclic quadrilateral property with other circle theorems in a single diagram to solve multi-step angle problems, explaining which theorem justifies each step.

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Cyclic Quadrilaterals

Cyclic Quadrilaterals

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