4MA1/2HR Jun 2025, Question 22: Stationary Points and Turning Points
Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 2HR (Higher) · Calculator · 5 marks
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The question, in short
Maximise the volume of a cuboid whose edges are x cm, x cm and (15 − 4x) cm.
Summarised in our own words. Use the official paper for the exact wording and the diagram.
Solution · 5 marks
- 1V = x × x × (15 − 4x) = 15x² − 4x³
- 2dV/dx = 30x − 12x²
- 330x − 12x² = 0 ⇒ 6x(5 − 2x) = 0
- 4x = 2.5 (x > 0)
- 5V = 2.5 × 2.5 × (15 − 10)
- 6= 31.25
Answer31.25
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