Paper 2 · Geometry Lesson 7 of 19

Geometry 7 – Proof of Theorem 4

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You’ll learn

  • Prove Theorem 4: the three angles in a triangle sum to 180°
  • Set out a proof under the five headings: Diagram, Given, To Prove, Construction, Proof
  • Draw a line through the apex parallel to the base and use alternate angles twice
  • Number the angles on your diagram and restate the target equation at the end

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