N2011 P2 Q3

N2011 P2 Q3

Junior College 2
11 marks

The function \(f\) is defined by \(f:x\mapsto\ln(2x+1)+3\), \(x\in\mathbb R\), \(x>-\frac12\).

  1. Find \(f^{-1}(x)\) and write down the domain and range of \(f^{-1}\).[4]
  2. Sketch on the same diagram the graphs of \(y=f(x)\) and \(y=f^{-1}(x)\), giving the equations of any asymptotes and the exact coordinates of any points where the curves cross the \(x\)- and \(y\)-axes.[4]
  3. Explain why the \(x\)-coordinates of the points of intersection of the curves in part (ii) satisfy the equation \(\ln(2x+1)=x-3\), and find the values of these \(x\)-coordinates, correct to 4 significant figures.[3]

Solution:

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Answer:(i) \(f^{-1}(x)=(\mathrm e^{x-3}-1)/2\), domain \(\mathbb R\), range \((-1/2,\infty)\). (iii) \(x=-0.4847,5.482\).

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