Enrich · Stage 4 · Properties of geometrical figures

Enrich Prove that any exterior angle of a triangle equals the sum of the 2 interior opposite angles

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• Interactive toolEnrichmentEnrich
  Mathigon: Properties of triangles
  Mathigon (Amplify) · Interactive (browser) · Free · Link checked 2026-10-15 · Hands-on, No prep
  Use it for: Extension: medians, perpendicular bisectors and triangle centres.
• Rich taskEnrichmentEarly finishersEnrich
  NRICH: Shapely Pairs
  NRICH (University of Cambridge) · Web page · Free · Link checked 2026-10-15 · Low floor high ceiling, Teacher notes
  Use it for: Low-floor, high-ceiling NRICH task extending this dot point; use for extension or a problem-solving lesson.