The diagram shows part of the curve y = 6/x. The points (1, 6) and (3, 2) lie on the curve. The shaded region is bounded by the curve and the lines y = 2 and x = 1. [Figure 8.1]
- (a)Find the volume generated when the shaded region is rotated through 360° about the y-axis.[5]
- (b)The tangent to the curve at a point X is parallel to the line y + 2x = 0. Show that X lies on the line y = 2x.[3]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.
- [*M1] Volume = π ∫ x²dy = π ∫ (6/y)²dy = π ∫ (36/y²)dy
- [A1] = π [-36/y]
- [DM1] Uses limits 2 to 6 correctly → (12π)
- [M1] Vol of cylinder = π.1².4 or ∫ 1²dy = [y] from 2 to 6
- [A1] Vol = 12π - 4π = 8π
- [B1] dy/dx = -6/x²
- [M1] -6/x² = -2 → x = √3
- [A1] y = 6/√3 = 2√3. Lies on y = 2x.
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