AMKSS 4AM 2022 Prelims P1 Q12

AMKSS 4AM 2022 Prelims P1 Q12

Secondary 4
7 marks

A curve is such that \(\frac{\mathrm{d}y}{\mathrm{d}x} = \frac{9}{(2x-1)^2}\), where \(x \neq \frac{1}{2}\). The point \((2, 12)\) lies on the curve.

  1. Find the equation of the curve.[3]
  2. Find the value of \(\frac{\mathrm{d}^2y}{\mathrm{d}x^2}\) when \(x = 0\).[2]
  3. A student concludes from (ii) that since the value of \(\frac{\mathrm{d}^2y}{\mathrm{d}x^2} > 0\) at \(x = 0\), hence there is a minimum point at \(x = 0\). State with reason and mathematical working whether the above conclusion is correct.[2]

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Answer:(i) \(y=-9/[2(2x-1)]+27/2\) for \(x>1/2\); an independent constant for \(x<1/2\). (ii) 36. (iii) No: \(y'(0)=9\ne0\).

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