4MA1/2F Jun 2020, Question 18: Angles in Parallel Lines
Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 2F (Foundation) · Calculator · 5 marks
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The question, in short
Parallelogram ABCD with angle BCD = 58°, DE = DF in isosceles triangle DEF, CDF and ADE straight. Find angle DEF, justifying each step.
Summarised in our own words. Use the official paper for the exact wording and the diagram.
Solution · 5 marks
- 1ADC = 180° − 58° = 122° (co-interior angles in a parallelogram add to 180°)
- 2EDF = ADC = 122° (vertically opposite angles are equal)
- 3DE = DF, so DEF = DFE (base angles of an isosceles triangle)
- 4DEF = (180° − 122°) ÷ 2 = 29 (angles in a triangle add to 180°)
Answer29
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