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4MA1/1H Jun 2019, Question 20: Alternate Segment Theorem

Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 1H (Higher) · Calculator · 5 marks

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The question, in short

Cyclic quadrilateral ABCD with tangent TDV at D, AB = AD and angle ADT = 71°. Find angle BCD, justifying each stage.

Summarised in our own words. Use the official paper for the exact wording and the diagram.

Solution · 5 marks

  1. 1Angle ABD = angle ADT = 71° (alternate segment theorem)
  2. 2AB = AD, so angle ADB = 71° (base angles of isosceles triangle)
  3. 3Angle BAD = 180° − 71° − 71° = 38° (angles in a triangle)
  4. 4Angle BCD = 180° − 38° = 142 (opposite angles of a cyclic quadrilateral)

Answer142

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