Paper 2 · Geometry Lesson 8 of 19

Geometry 8 – Proof of theorem 6

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You’ll learn

  • Prove Theorem 6: the exterior angle equals the sum of the two interior opposite angles
  • Combine two 180° equations (straight angle + Theorem 4) and cancel the shared angle
  • Apply the chronological rule: prove Theorem N using only Theorems 1 to N−1
  • Restate the conclusion in the original notation to secure the final marks

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