2021 HCI P2 Q2

2021 HCI P2 Q2

8 marks
Prelims
  1. An ellipse of equation \(\frac{{{x}^{2}}}{{{a}^{2}}}+\frac{{{y}^{2}}}{{{b}^{2}}}=1\), where \(0 < b < a\), has two points called foci \({{F}_{1}}\left( -c,0 \right)\) and \({{F}_{2}}\left( c,0 \right)\). The definition of the ellipse is such that for every point \(P\) on the ellipse, the sum of the distance of \(P\) to \({{F}_{1}}\) and \({{F}_{2}}\) is always a constant \(k\).
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    1. By considering one of the \(x\)-intercepts of the ellipse, determine the value of \(k\) in terms of \(a\) and/or \(b\).[2]
    2. By considering another suitable point on the ellipse, find \(c\) in terms of \(a\) and \(b\).[2]
  2. A hyperbola with equation \({{\left( y-h \right)}^{2}}-1=\frac{1}{4}{{\left( x-k \right)}^{2}}\) has \(y=\frac{1}{2}x+\frac{3}{2}\) as one of its asymptotes, and the point \(\left( 1,3 \right)\) is on the hyperbola. Find the values of \(h\) and \(k\).[4]

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Answer:(a)(i) \(k=2a\) (a)(ii) \(c=\sqrt{a^2-b^2}\) (b) \(h=2\), \(k=1\)

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