The equation of a curve is y = √(8x – x²). Find
- (i)an expression for dy/dx, and the coordinates of the stationary point on the curve,[4]
- (ii)the volume obtained when the region bounded by the curve and the x-axis is rotated through 360° about the x-axis.[4]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2011). The mark or mark type is shown in brackets.
- [4] dy/dx = ½(8x – x²)⁻¹/² × (8 – 2x)
- [4] = 0 when x = 4.
- [4] → (4,4)
- [4] y = 0 when x = 0 or 8
- [4] Vol = π ∫(8x - x²) dx
- [4] = π [4x² - x³/3]
- [4] 256π/3
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