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O-LevelAdditional MathematicsDifferentiation and integration4037/11 · May/June 2020 · Q34 Marks

The radius, r cm, of a circle is increasing at the rate of 5 cms⁻¹. Find, in terms of π, the rate at which the area of the circle is increasing when r = 3.

(a)The radius, r cm, of a circle is increasing at the rate of 5 cms⁻¹. Find, in terms of π, the rate at which the area of the circle is increasing when r = 3.[4]

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

[B1] dr/dt = 5
[B1] dA/dr = 2πr
[M1] Use of the chain rule, may be implied by 5 × 6π
[A1] dA/dt = 30π

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About this question

Topic: Differentiation and integration, O-Level Additional Mathematics (syllabus 4037). Structured question, 4 marks.
Source: O-Level Additional Mathematics, May/June 2020 Paper 1 Variant 1, question 3.

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