Solve equation involving |f(x)| and g(x)

Solve equation where one side is modulus of a function and other side is non-modulus function, requiring graphical or algebraic analysis, e.g. |4e^(2x)-25| = 2x+43.

3 questions · Standard +0.3

Sort by: Default | Easiest first | Hardest first
Edexcel P3 2023 October Q9
9 marks Standard +0.3
  1. In this question you must show all stages of your working.
Solutions relying on calculator technology are not acceptable. \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{08291ac1-bdd4-4241-8959-7c89318fa5eb-26_613_729_386_667} \captionsetup{labelformat=empty} \caption{Figure 2}
\end{figure} Figure 2 shows a sketch of the curve with equation $$y = | 2 - 4 \ln ( x + 1 ) | \quad x > k$$ where \(k\) is a constant.
Given that the curve
  • has an asymptote at \(x = k\)
  • cuts the \(y\)-axis at point \(A\)
  • meets the \(x\)-axis at point \(B\) as shown in Figure 2,
    1. state the value of \(k\)
      1. find the \(y\) coordinate of \(A\)
      2. find the exact \(x\) coordinate of \(B\)
    2. Using algebra and showing your working, find the set of values of \(x\) such that
$$| 2 - 4 \ln ( x + 1 ) | > 3$$
Edexcel C3 2016 June Q4
11 marks Standard +0.3
4. \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{d3ba2776-eedb-48f0-834f-41aa454afba3-06_675_1118_205_406} \captionsetup{labelformat=empty} \caption{Figure 1}
\end{figure} Figure 1 shows a sketch of part of the curve with equation \(y = g ( x )\), where $$\mathrm { g } ( x ) = \left| 4 \mathrm { e } ^ { 2 x } - 25 \right| , \quad x \in \mathbb { R }$$ The curve cuts the \(y\)-axis at the point \(A\) and meets the \(x\)-axis at the point \(B\). The curve has an asymptote \(y = k\), where \(k\) is a constant, as shown in Figure 1
  1. Find, giving each answer in its simplest form,
    1. the \(y\) coordinate of the point \(A\),
    2. the exact \(x\) coordinate of the point \(B\),
    3. the value of the constant \(k\). The equation \(\mathrm { g } ( x ) = 2 x + 43\) has a positive root at \(x = \alpha\)
  2. Show that \(\alpha\) is a solution of \(x = \frac { 1 } { 2 } \ln \left( \frac { 1 } { 2 } x + 17 \right)\) The iteration formula $$x _ { n + 1 } = \frac { 1 } { 2 } \ln \left( \frac { 1 } { 2 } x _ { n } + 17 \right)$$ can be used to find an approximation for \(\alpha\)
  3. Taking \(x _ { 0 } = 1.4\) find the values of \(x _ { 1 }\) and \(x _ { 2 }\) Give each answer to 4 decimal places.
  4. By choosing a suitable interval, show that \(\alpha = 1.437\) to 3 decimal places. \includegraphics[max width=\textwidth, alt={}, center]{d3ba2776-eedb-48f0-834f-41aa454afba3-07_2258_47_315_37}
OCR H240/03 2021 November Q4
5 marks Standard +0.3
4
  1. Sketch, on a single diagram, the following graphs.
    • \(y = | x - 1 |\)
    • \(y = \frac { k } { x }\), where \(k\) is a negative constant
    • Hence explain why the equation \(x | x - 1 | = k\) has exactly one real root for any negative value of \(k\).
    • Determine the real root of the equation \(x | x - 1 | = - 6\).