Linear relationship between log variables

Given a linear graph relating log(y) and log(x) or similar, find equation or express y in form px^q.

4 questions · Moderate -0.5

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Edexcel P3 2020 January Q3
5 marks Moderate -0.8
3. \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{1c700103-ecab-4a08-b411-3f445ed88885-08_599_883_299_536} \captionsetup{labelformat=empty} \caption{Figure 1}
\end{figure} Figure 1 shows a linear relationship between \(\log _ { 10 } y\) and \(\log _ { 10 } x\) The line passes through the points \(( 0,4 )\) and \(( 6,0 )\) as shown.
  1. Find an equation linking \(\log _ { 10 } y\) with \(\log _ { 10 } x\)
  2. Hence, or otherwise, express \(y\) in the form \(p x ^ { q }\), where \(p\) and \(q\) are constants to be found.
Edexcel P3 2023 June Q2
6 marks Moderate -0.3
2. \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{bef290fb-fbac-4c9c-981e-5e323ac7182e-04_814_839_242_614} \captionsetup{labelformat=empty} \caption{Figure 1}
\end{figure} Figure 1 shows the linear relationship between \(\log _ { 6 } T\) and \(\log _ { 6 } x\) The line passes through the points \(( 0,4 )\) and \(( 2,0 )\) as shown.
    1. Find an equation linking \(\log _ { 6 } T\) and \(\log _ { 6 } x\)
    2. Hence find the exact value of \(T\) when \(x = 216\)
  1. Find an equation, not involving logs, linking \(T\) with \(x\)
Edexcel P3 2024 June Q3
6 marks Moderate -0.5
  1. (i) The variables \(x\) and \(y\) are connected by the equation
$$y = \frac { 10 ^ { 6 } } { x ^ { 3 } } \quad x > 0$$ Sketch the graph of \(\log _ { 10 } y\) against \(\log _ { 10 } x\) Show on your sketch the coordinates of the points of intersection of the graph with the axes.
(ii) \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{5a695b86-1660-4c06-ac96-4cdb07af9a2e-08_888_885_744_552} \captionsetup{labelformat=empty} \caption{Figure 2}
\end{figure} Figure 2 shows the linear relationship between \(\log _ { 3 } N\) and \(t\).
Show that \(N = a b ^ { t }\) where \(a\) and \(b\) are constants to be found.
CAIE P2 2024 November Q1
5 marks Moderate -0.3
The variables \(x\) and \(y\) satisfy the equation \(a^{2y} = e^{3x+k}\), where \(a\) and \(k\) are constants. The graph of \(y\) against \(x\) is a straight line.
  1. Use logarithms to show that the gradient of the straight line is \(\frac{3}{2\ln a}\). [1]
  2. Given that the straight line passes through the points \((0.4, 0.95)\) and \((3.3, 3.80)\), find the values of \(a\) and \(k\). [4]