In this question all lengths are in centimetres. A closed cylinder has base radius r, height h and volume V. It is given that the total surface area of the cylinder is 600π and that V, r and h can vary.
- (i)Show that V = 300πr-πr³.[3]
- (ii)Find the stationary value of V and determine its nature.[5]
Mark scheme
Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.
- [B1] 600π = 2πr² + 2πrh
- [M1] making h subject from a two term expression for SA.
- [A1] correct substitution and manipulation to obtain given answer
- [M1] differentiation of given formula to A+Br²
- [M1] equating to zero and attempt to solve
- [A1] r = 10
- [A1] V = 2000π or 6280 or 6283
- [B1] cao for d²V/dr² = -6πr, d²V/dr² = −60π or other correct method leading to maximum
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