2024 DHS P1 Q5

2024 DHS P1 Q5

7 marks
Prelims

The function \(\mathrm{f}\) is defined by

\(\mathrm{f}:x\mapsto \frac{{{x}^{2}}}{x-4}\), \(x\in \mathbb{R}\), \(4 < x \le 8\)

  1. Find \({{\mathrm{f}}^{-1}}\left( x \right)\) and write down the domain of \({{\mathrm{f}}^{-1}}\). On the same axes, sketch the graphs of \(y=\mathrm{f}\left( x \right)\) and \(y={{\mathrm{f}}^{-1}}\left( x \right)\).[4]
  2. The region \(R\) is bounded by the curve \(y={{\mathrm{f}}^{-1}}\left( x \right)\), the lines \(y=5\), \(y=8\) and the \(y\)-axis. Find the exact area of \(R\).[3]

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Answer:(a) \(\displaystyle \mathrm{f}^{-1}(x)=\frac{x-\sqrt{x^2-16x}}{2}\), domain \([16,\infty)\) (b) \(\displaystyle\frac{63}{2}+32\ln2\text{ units}^2\)

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