The point P (2, 1) lies on the curve with equation `x³ - 2y³ = 3xy`.
- (i)the value of `dy/dx` at P,[3]
- (ii)the value of `d²y/dx²` at P.[4]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2011). The mark or mark type is shown in brackets.
- [B1B1] One mark for each side. 3x² - 6y² y' = 3y + 3xy'
- [B1√] Substitutes (2,1) 12 - 6y' = 3 + 6y' ⇒ y' = 3/4
- [B1B1B1] One mark for differentiating both 1st and 3rd terms. One mark for each of 2nd and 4th terms. 6x - {6y²y'' + 12y(y')²}=3y' + 3y' + 3xy''
- [B1] Substitute (2,1) and y'(2) = 3/4 12 - (6y'' + 27/4) = 3/4 + 3/4 + 6y'' ⇒ 12y'' = -1/16 ⇒ y'' = -1/16
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