AQA C3 2013 June — Question 8 12 marks

Exam BoardAQA
ModuleC3 (Core Mathematics 3)
Year2013
SessionJune
Marks12
PaperDownload PDF ↗
TopicComposite & Inverse Functions
TypeFind composite function expression
DifficultyModerate -0.3 This is a standard C3 composite and inverse functions question with routine algebraic manipulation. Finding the inverse of a logarithmic function, composing functions, and solving the resulting equation are all textbook exercises requiring no novel insight, though the multi-part structure and algebraic manipulation (especially simplifying gf(x) to the required form) place it slightly below average difficulty.
Spec1.02v Inverse and composite functions: graphs and conditions for existence1.06d Natural logarithm: ln(x) function and properties

8 The curve with equation \(y = \mathrm { f } ( x )\), where \(\mathrm { f } ( x ) = \ln ( 2 x - 3 ) , x > \frac { 3 } { 2 }\), is sketched below. \includegraphics[max width=\textwidth, alt={}, center]{063bbfa5-df49-44a1-8143-5e076397f63f-08_630_1173_424_443}
  1. The inverse of f is \(\mathrm { f } ^ { - 1 }\).
    1. Find \(\mathrm { f } ^ { - 1 } ( x )\).
    2. State the range of \(\mathrm { f } ^ { - 1 }\).
    3. Sketch, on the axes given on page 9 , the curve with equation \(y = \mathrm { f } ^ { - 1 } ( x )\), indicating the value of the \(y\)-coordinate of the point where the curve intersects the \(y\)-axis.
      (2 marks)
  2. The function g is defined by $$\mathrm { g } ( x ) = \mathrm { e } ^ { 2 x } - 4 , \text { for all real values of } x$$
    1. Find \(\mathrm { gf } ( x )\), giving your answer in the form \(( a x - b ) ^ { 2 } - c\), where \(a , b\) and \(c\) are integers.
    2. Write down an expression for \(\mathrm { fg } ( x )\), and hence find the exact solution of the equation \(\operatorname { fg } ( x ) = \ln 5\). \includegraphics[max width=\textwidth, alt={}, center]{063bbfa5-df49-44a1-8143-5e076397f63f-09_1079_1422_233_358}

8 The curve with equation $y = \mathrm { f } ( x )$, where $\mathrm { f } ( x ) = \ln ( 2 x - 3 ) , x > \frac { 3 } { 2 }$, is sketched below.\\
\includegraphics[max width=\textwidth, alt={}, center]{063bbfa5-df49-44a1-8143-5e076397f63f-08_630_1173_424_443}
\begin{enumerate}[label=(\alph*)]
\item The inverse of f is $\mathrm { f } ^ { - 1 }$.
\begin{enumerate}[label=(\roman*)]
\item Find $\mathrm { f } ^ { - 1 } ( x )$.
\item State the range of $\mathrm { f } ^ { - 1 }$.
\item Sketch, on the axes given on page 9 , the curve with equation $y = \mathrm { f } ^ { - 1 } ( x )$, indicating the value of the $y$-coordinate of the point where the curve intersects the $y$-axis.\\
(2 marks)
\end{enumerate}\item The function g is defined by

$$\mathrm { g } ( x ) = \mathrm { e } ^ { 2 x } - 4 , \text { for all real values of } x$$
\begin{enumerate}[label=(\roman*)]
\item Find $\mathrm { gf } ( x )$, giving your answer in the form $( a x - b ) ^ { 2 } - c$, where $a , b$ and $c$ are integers.
\item Write down an expression for $\mathrm { fg } ( x )$, and hence find the exact solution of the equation $\operatorname { fg } ( x ) = \ln 5$.\\
\includegraphics[max width=\textwidth, alt={}, center]{063bbfa5-df49-44a1-8143-5e076397f63f-09_1079_1422_233_358}
\end{enumerate}\end{enumerate}

\hfill \mbox{\textit{AQA C3 2013 Q8 [12]}}