4024/11 May/Jun 2020, Question 5: Angles in a Triangle
Cambridge O Level Mathematics 4024 · Paper 11 (Non-calculator) · Non-calculator · 2 marks
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The question, in short
In the diagram, isosceles triangle ABC has AC = CB and equilateral triangle BDE has equal sides; D lies on AB and CE, angle BAC = 28°. Find x, the angle at C between CE and CB.
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Solution · 2 marks
- 1Triangle ABC is isosceles (AC = CB), so angle ABC = angle BAC = 28°
- 2Triangle BDE is equilateral, so angle BDE = 60°
- 3Angle BDC = 180 − 60 = 120° (angles on a straight line CDE)
- 4x = 180 − 28 − 120 = 32 (angles in triangle BDC)
Answer32
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