A-LevelMathematicsDifferentiation9709/12 · May/June 2015 · Q45 Marks
Variables u, x and y are such that u = 2x(y – x) and x + 3y = 12. Express u in terms of x and hence find the stationary value of u.
- Variables u, x and y are such that u = 2x(y – x) and x + 3y = 12. Express u in terms of x and hence find the stationary value of u.[5]
Mark scheme
Marking points from the official mark scheme (May/June 2015). The mark or mark type is shown in brackets.
- [M1 A1] u = 2x((12-x)/3 – x) Expresses u in terms of x
- [M1] du/dx = 8 – (16/3)x Differentiate candidate's quadratic, sets to 0 + attempt to find x, or other valid method
- [A1] = 0 when x = 1 ½
- [A1] → u = 6 Co Complete method that leads to u
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