2010 HCI P1 Q3

2010 HCI P1 Q3

6 marks
Prelims

The function \(\mathrm{f}\) and \(\mathrm{g}\) are defined as follows:

\(\mathrm{f}:x\mapsto {{\left( 2x-1 \right)}^{2}}-2\), \( \qquad x<-1\)

\(\mathrm{g}:x\mapsto \ln \left( x+a \right)\), \(x>-1\)

  1. Define \({{\mathrm{f}}^{-1}}\) in a similar form.[3]
  2. State the value of \(a\) such that the range of \(\mathrm{g}\) is \(\left( 0,\infty \right)\).[1]
  3. Show that the composite function \(\mathrm{gf}\) exists, and find the range of \(\mathrm{gf}\), giving your answer in terms of \(a\).[2]

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Answer:(a) \({{\mathrm{f}}^{-1}}:x\mapsto \frac{1}{2}-\frac{1}{2}\sqrt{x+2},x>7\) (b) \(a=2\) (c) \({{R}_{\mathrm{fg}}}=\left( \ln \left( a+7 \right),\infty \right)\)

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