EITHER The curve C is defined parametrically by x = 18t - t² and y = 8t³, where 0 < t < 4.
- (i)Show that at all points of C, d²y/dx² = 3(9+t) / (2t²(9-t)³).[4]
- (ii)Show that the mean value of d²y/dx² with respect to x over the interval 0 < x ≤ 56 is 3/70.[4]
- (iii)Find the area of the surface generated when C is rotated through 2π radians about the x-axis, showing full working.[6]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.
- [B1] AEF.
- [M1] Uses chain rule again to find second derivative.
- [dM1] Uses quotient (or product rule)
- [A1] AG.
- [B1] Uses correct formula for mean value
- [M1] Finding limits correctly
- [M1] Using expression
- [A1] Inserts correct values of t and obtains answer (AG.)
- [M1A1] Simplifies (dx/dt)² + (dy/dt)²
- [M1A1] Uses 2π ∫ y ds / dt dt.
- [M1] Integrates term by term.
- [A1] Accept exact answer or decimal rounding to 15300.
Write your answer and get it marked
On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.
Sign up free →