Paper 2 · Geometry ⏱ Tested in 4 exam questions since 2022 Lesson 11 of 19

Geometry 11 – Proof of theorem 19

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You’ll learn

  • Prove Theorem 19: the angle at the centre is twice the angle at the edge on the same arc
  • Draw the diameter through A so two radii create isosceles triangles on each side
  • Apply Theorem 6 plus isosceles base angles to get ∠1 = 2·∠4, then close with 'similarly'

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