OCR C3 2013 January — Question 7

Exam BoardOCR
ModuleC3 (Core Mathematics 3)
Year2013
SessionJanuary
TopicFixed Point Iteration

7
  1. By sketching the curves \(y = \ln x\) and \(y = 8 - 2 x ^ { 2 }\) on a single diagram, show that the equation $$\ln x = 8 - 2 x ^ { 2 }$$ has exactly one real root.
  2. Explain how your diagram shows that the root is between 1 and 2 .
  3. Use the iterative formula $$x _ { n + 1 } = \sqrt { 4 - \frac { 1 } { 2 } \ln x _ { n } } ,$$ with a suitable starting value, to find the root. Show all your working and give the root correct to 3 decimal places.
  4. The curves \(y = \ln x\) and \(y = 8 - 2 x ^ { 2 }\) are each translated by 2 units in the positive \(x\)-direction and then stretched by scale factor 4 in the \(y\)-direction. Find the coordinates of the point where the new curves intersect, giving each coordinate correct to 2 decimal places.
    \includegraphics[max width=\textwidth, alt={}, center]{b8ff33d4-dfe5-4067-855e-86d5765cc249-3_389_917_1117_557} The diagram shows the curve with equation $$x = ( y + 4 ) \ln ( 2 y + 3 ) .$$ The curve crosses the \(x\)-axis at \(A\) and the \(y\)-axis at \(B\).
  5. Find an expression for \(\frac { \mathrm { d } x } { \mathrm {~d} y }\) in terms of \(y\).
  6. Find the gradient of the curve at each of the points \(A\) and \(B\), giving each answer correct to 2 decimal places.