2015 SAJC P1 Q5

2015 SAJC P1 Q5

5 marks
Prelims

The ellipse \({{C}_{1}}\) with the equation \(\frac{{{x}^{2}}}{{{6}^{2}}}+\frac{{{y}^{2}}}{{{3}^{2}}}=1\) is transformed by a stretch with scale factor \(k\) parallel to the \(x\)-axis, followed by a translation of \(m\) units in the positive \(x\)-direction, followed by a translation of \(n\) units in the negative \(y\)-direction, to form \({{C}_{2}}\).

  1. Find the equation of \({{C}_{2}}\) in terms of \(k\), \(m\) and \(n\).[3]
  2. Given that \({{C}_{2}}\) is a circle centred at \(\left( 4,-7 \right)\), find the values of \(k\), \(m\) and \(n\).[2]

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Answer:(i) \({C_2 : \frac{(x-m)^2}{(6k)^2} + \frac{(y+n)^2}{3^2} = 1}\) (ii) \({k = \frac{1}{2}\;, m = 4\;, n = 7}\)

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