Edexcel C3 2011 January — Question 5

Exam BoardEdexcel
ModuleC3 (Core Mathematics 3)
Year2011
SessionJanuary
TopicDifferentiation Applications
TypeFind stationary points

5. \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{3ff6824f-9fbf-4b5b-8bab-91332c549b36-08_624_1054_274_447} \captionsetup{labelformat=empty} \caption{Figure 1}
\end{figure} Figure 1 shows a sketch of part of the curve with equation \(y = \mathrm { f } ( x )\), where $$\mathrm { f } ( x ) = ( 8 - x ) \ln x , \quad x > 0$$ The curve cuts the \(x\)-axis at the points \(A\) and \(B\) and has a maximum turning point at \(Q\), as shown in Figure 1.
  1. Write down the coordinates of \(A\) and the coordinates of \(B\).
  2. Find f'(x).
  3. Show that the \(x\)-coordinate of \(Q\) lies between 3.5 and 3.6
  4. Show that the \(x\)-coordinate of \(Q\) is the solution of $$x = \frac { 8 } { 1 + \ln x }$$ To find an approximation for the \(x\)-coordinate of \(Q\), the iteration formula $$x _ { n + 1 } = \frac { 8 } { 1 + \ln x _ { n } }$$ is used.
  5. Taking \(x _ { 0 } = 3.55\), find the values of \(x _ { 1 } , x _ { 2 }\) and \(x _ { 3 }\). Give your answers to 3 decimal places.