0580/12 Oct/Nov 2021, Question 18: Angles in a Triangle
Cambridge IGCSE Mathematics 0580 · Paper 12 (Core) · Calculator · 3 marks
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The question, in short
Using a quadrilateral ABCD with diagonal AC, where AB, AC and AD are equal, angle DAB is 86° and angle ADC is 58°, find x, the angle at B.
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Solution · 3 marks
- 1AC = AD, so angle ACD = angle ADC = 58°
- 2Angle DAC = 180 − 58 − 58 = 64°
- 3Angle CAB = 86 − 64 = 22°
- 4AB = AC, so angle ACB = x and x + x + 22 = 180
- 52x = 158, x = 79
Answer79
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