4PM1/02 Jun 2019, Question 2: Connected Rates of Change and Small Changes
Pearson Edexcel International GCSE Further Pure Mathematics 4PM1 · Paper 2 · Calculator · 6 marks
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The question, in short
Oil spreads in a circular pool with surface area growing at 8 cm²/s. Find the rate of increase of the radius, in cm/s to 3 significant figures, when the area is 50 cm².
Summarised in our own words. Use the official paper for the exact wording and any diagrams.
Solution · 6 marks
- 1dA/dt = 8
- 2A = πr², dA/dr = 2πr
- 3A = 50: r = √(50/π) = 3.989…
- 4dr/dt = (dr/dA) × (dA/dt) = 8/(2π × 3.989…)
- 5= 0.319 cm/s
Answer0.319 cm/s
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