2019 ASRJC Promo Q3

2019 ASRJC Promo Q3

3 marks
Promo

A curve \(C\) has equation \({{\left( \ln y \right)}^{2}}-3xy+{{x}^{2}}-4=0\).

  1. Show that \(\frac{\mathrm{d}y}{\mathrm{d}x}=\frac{\left( 3y-2x \right)y}{2\ln y-3xy}\).[3]
  2. It is given that \(C\) contains the point \(A\) with coordinates \(\left( \alpha ,1 \right)\) where \(\alpha <0\).
    Find the value of \(\alpha \) and hence the equation of the normal to \(C\) at the point \(A\).[3]

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Answer:(i) \(\frac{dy}{dx}=\frac{(3y-2x)y}{2\ln y-3xy}\); (ii) \(y=-\frac35x+\frac25\)

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