O-LevelMathematicsGeometry4024/11 · May/June 2021 · Q173 Marks

The diagram shows an isosceles triangle ABC where AB = AC. D is a point on AC such that angle ADB = 90°. E is a point on AB such that angle AEC = 90°. Show that triangles ADB and AEC are congruent. Give a reason for each statement you make. [Figure 17]

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Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

[3] Angle A is common
AÊC = ADB [= 90°] Given
AB = AC Given
Triangle ADB is congruent to triangle AEC AAS
B2 for two pairs of equal sides/angles with correct reasons
B1 for one pair of equal sides/angles with correct reason or for two appropriate pairs with no or incorrect reasons

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Topic: Geometry, O-Level Mathematics (syllabus 4024). Structured question, 3 marks.
Source: O-Level Mathematics, May/June 2021 Paper 1 Variant 1, question 17.

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