2026 ACJC P1 Q5

2026 ACJC P1 Q5

Junior College 2
8 marks

The function \(\mathrm{f}\) is defined by \(\mathrm{f}:x\mapsto\dfrac{kx+2}{2-x}\), for \(x\in\mathbb{R}\), \(x\ne2\).

  1. If the point with coordinates \((-7,4)\) lies on the curve \(y=\mathrm{f}^{-1}(x)\), show that \(k=3\).[1]
  2. Use \(k=3\) for the rest of this question.
    The function \(\mathrm{g}\) is defined by \(\mathrm{g}:x\mapsto\mathrm{f}(|x|)\), for \(x\in\mathbb{R}\), \(x\leq0\) and \(x\ne-2\).
    Sketch the graph of \(y=\mathrm{g}(x)\), stating the axial intercept and the equations of asymptotes.[3]
  3. Find \(\mathrm{g}^{-1}(x)\), stating its domain.[4]

Solution:

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Answer:(a) \(k=3\) (b) intercept \((0,1)\); asymptotes \(x=-2\), \(y=-3\) (c) \(\mathrm{g}^{-1}(x)=\frac{2(1-x)}{x+3}\), domain \(( -\infty,-3)\cup[1,\infty)\)

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