2025 IGCSE Additional Mathematics May/June 0606/12 Q9

2025 IGCSE Additional Mathematics May/June 0606/12 Q9

8 marks

It is given that \(\mathrm f(x)=2\ln(3x-4)\), for \(x>a\), and that \(\mathrm f^{-1}\) exists.

  1. Find the least possible value of \(a\).[1]
  2. For your value of \(a\), find the range of \(\mathrm f\).[1]
  3. For your value of \(a\), find an expression for \(\mathrm f^{-1}(x)\).[2]
  4. It is given that the equation \(\mathrm f(x)=\mathrm f^{-1}(x)\) has two roots.
    For your value of \(a\), sketch the graphs of \(y=\mathrm f(x)\) and \(y=\mathrm f^{-1}(x)\) on the axes.
    Label each graph.
    State the intercepts of each graph with the axes.
    State the equations of any asymptotes.[4]

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Answer:(a) \(a=\dfrac43\) (b) \(\mathbb R\) (c) \(\dfrac{\mathrm e^{x/2}+4}3\) (d) Sketch shown; \(\mathrm f\): intercept \(\left(\dfrac53,0\right)\), asymptote \(x=\dfrac43\). Inverse: intercept \(\left(0,\dfrac53\right)\), asymptote \(y=\dfrac43\).

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