Solutions from graphical analysis

Questions asking to determine the number of solutions or range of parameter values by analyzing a given graph, using horizontal line intersection counting.

7 questions

CAIE P1 2021 November Q5
5
\includegraphics[max width=\textwidth, alt={}, center]{af7aeda9-2ded-4db4-9ff3-ed6adc67859f-07_778_878_255_630} The diagram shows part of the graph of \(y = a \cos ( b x ) + c\).
  1. Find the values of the positive integers \(a , b\) and \(c\).
  2. For these values of \(a\), \(b\) and \(c\), use the given diagram to determine the number of solutions in the interval \(0 \leqslant x \leqslant 2 \pi\) for each of the following equations.
    1. \(a \cos ( b x ) + c = \frac { 6 } { \pi } x\)
    2. \(a \cos ( b x ) + c = 6 - \frac { 6 } { \pi } x\)
      The diagram shows a metal plate \(A B C\) in which the sides are the straight line \(A B\) and the arcs \(A C\) and \(B C\). The line \(A B\) has length 6 cm . The arc \(A C\) is part of a circle with centre \(B\) and radius 6 cm , and the arc \(B C\) is part of a circle with centre \(A\) and radius 6 cm .
CAIE P1 2019 June Q9
9
\includegraphics[max width=\textwidth, alt={}, center]{f462c036-45d3-4679-ad53-4edbf99df76d-14_558_963_260_589} The function \(\mathrm { f } : x \mapsto p \sin ^ { 2 } 2 x + q\) is defined for \(0 \leqslant x \leqslant \pi\), where \(p\) and \(q\) are positive constants. The diagram shows the graph of \(y = \mathrm { f } ( x )\).
  1. In terms of \(p\) and \(q\), state the range of f .
  2. State the number of solutions of the following equations.
    (a) \(\mathrm { f } ( x ) = p + q\)
    (b) \(\mathrm { f } ( x ) = q\)
    (c) \(\mathrm { f } ( x ) = \frac { 1 } { 2 } p + q\)
  3. For the case where \(p = 3\) and \(q = 2\), solve the equation \(\mathrm { f } ( x ) = 4\), showing all necessary working.
Edexcel P1 2022 October Q7
7. \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{db979349-3415-420f-a39f-8cc8c24a69d0-16_732_1071_248_497} \captionsetup{labelformat=empty} \caption{Figure 1}
\end{figure} Figure 1 shows the curve with equation \(y = \mathrm { f } ( x )\).
The points \(P ( - 4,6 ) , Q ( - 1,6 ) , R ( 2,6 )\) and \(S ( 3,6 )\) lie on the curve.
  1. Using Figure 1, find the range of values of \(x\) for which $$\mathrm { f } ( x ) < 6$$
  2. State the largest solution of the equation $$f ( 2 x ) = 6$$
    1. Sketch the curve with equation \(y = \mathrm { f } ( - x )\). On your sketch, state the coordinates of the points to which \(P , Q , R\) and \(S\) are transformed.
    2. Hence find the set of values of \(x\) for which $$f ( - x ) \geqslant 6 \text { and } x < 0$$
OCR C1 Q6
6.
\includegraphics[max width=\textwidth, alt={}, center]{00364339-8108-4031-8e67-6100810e8297-2_549_885_251_370} The diagram shows the graph of \(y = \mathrm { f } ( x )\).
  1. Write down the number of solutions that exist for the equation
    1. \(\mathrm { f } ( x ) = 1\),
    2. \(\mathrm { f } ( x ) = - x\).
  2. Labelling the axes in a similar way, sketch on separate diagrams the graphs of
    1. \(\quad y = \mathrm { f } ( x - 2 )\),
    2. \(y = \mathrm { f } ( 2 x )\).
Edexcel C1 Q8
8. \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{d05cfae5-1d1d-4c90-80df-2975b9481c82-3_522_844_1235_379} \captionsetup{labelformat=empty} \caption{Figure 1}
\end{figure} Figure 1 shows the graph of \(y = \mathrm { f } ( x )\).
  1. Write down the number of solutions that exist for the equation
    1. \(\mathrm { f } ( x ) = 1\),
    2. \(\mathrm { f } ( x ) = - x\).
  2. Labelling the axes in a similar way, sketch on separate diagrams the graphs of
    1. \(\quad y = \mathrm { f } ( x - 2 )\),
    2. \(y = \mathrm { f } ( 2 x )\).
SPS SPS SM Pure 2024 June Q6
6. \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{b063f4ea-372b-4193-b8fe-a9f8017d7349-12_735_1081_239_500} \captionsetup{labelformat=empty} \caption{Figure 1}
\end{figure} Figure 1 shows the curve with equation \(y = \mathrm { f } ( x )\).
The points \(P ( - 4,6 ) , Q ( - 1,6 ) , R ( 2,6 )\) and \(S ( 3,6 )\) lie on the curve.
  1. Using Figure 1, find the range of values of \(x\) for which $$f ( x ) < 6$$
  2. State the largest solution of the equation $$f ( 2 x ) = 6$$
    1. Sketch the curve with equation \(y = \mathrm { f } ( - x )\). On your sketch, state the coordinates of the points to which \(P , Q , R\) and \(S\) are transformed.
    2. Hence, using set notation, find the set of values of \(x\) for which $$f ( - x ) \geq 6 \text { and } x < 0$$
SPS SPS FM 2025 October Q1
6 marks
  1. The graph of \(y = f ( x )\), defined for \(- 3 \leq x \leq 7\), is shown below, along with the coordinates of the turning points and endpoints:
    \includegraphics[max width=\textwidth, alt={}, center]{9345ffb5-b2ec-4366-8956-c8d766bacbd4-02_1157_1584_1539_319}
    1. How many solutions are there to \(f ( x ) = 1\) ?
    2. If \(f ( x ) = k\) has three distinct solutions, find the possible values of \(k\).
    3. How many solutions are there to \(f \left( x ^ { 2 } \right) = 1\) ?
    4. If \(f \left( x ^ { 2 } \right) = k\) has five distinct solutions, find the value of \(k\).
    5. How many solutions are there to \([ f ( x ) ] ^ { 2 } = 2\) ?
    6. If \([ f ( x ) ] ^ { 2 } = k\) has six distinct solutions, find the range of possible values of \(k\).
    7. How many solutions are there to \(\log _ { 2 } f ( x ) = - 2025\) ?
    8. How many solutions are there to \(\log _ { 2 } \left( [ f ( x ) ] ^ { 2 } \right) = 0\) ?
    9. Show that, if \(n\) is a non-negative integer, \(4 ^ { 3 n } + 5 ^ { 2 n + 2 }\) cannot be a prime.
      [0pt] [6]
      [0pt] [BLANK PAGE]
    10. All of these questions concern the curve \(y = g ( x )\).
    Part of the graph of \(y = g ^ { \prime \prime } ( x )\) is shown below:
    \includegraphics[max width=\textwidth, alt={}, center]{9345ffb5-b2ec-4366-8956-c8d766bacbd4-06_1083_1744_258_258} You are given that \(y = g ( x )\) has exactly two local minima and one local maximum in this range.
  2. Identify which of the labelled points could correspond to the local maximum.
  3. Identify two of the labelled points which could correspond to the local minima. There is more than one possible pair of answers but you are only required to give one.
  4. Identify all of the labelled points which correspond to points of inflection.
  5. As \(x \rightarrow - \infty , g ^ { \prime \prime } ( x ) \rightarrow 0\). What does this tell you about the shape of the curve \(y = g ( x )\) as \(x \rightarrow - \infty\) ?
    [0pt] [BLANK PAGE] \section*{4. In this question you must show detailed reasoning} The non-zero coefficients of \(x , x ^ { 2 }\) and \(x ^ { 3 }\) in the expansion of \(( 1 + x ) ^ { n }\) form the first, second and third terms of an arithmetic sequence (in that order).
  6. Determine the possible value(s) of \(n\).
  7. For the same value(s) of \(n\), there is another value of \(a\) for which \(( 1 + a x ) ^ { n }\) has this property. Determine this value of \(a\).