4MA1/2H Jun 2019, Question 18: Stationary Points and Turning Points
Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 2H (Higher) · Calculator · 5 marks
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The question, in short
A cuboid has two edges of x cm and a third of (12 − 3x) cm. Work out the largest possible value of its total surface area A, in cm².
Summarised in our own words. Use the official paper for the exact wording and the diagram.
Solution · 5 marks
- 1Top and bottom: 2 × x² = 2x²
- 2Four side faces: 4 × x(12 − 3x) = 48x − 12x²
- 3A = 2x² + 48x − 12x² = 48x − 10x²
- 4dA/dx = 48 − 20x = 0, so x = 2.4
- 5A = 48 × 2.4 − 10 × 2.4² = 115.2 − 57.6 = 57.6
Answer57.6
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