2024 ACS(BR) P2 Q7

2024 ACS(BR) P2 Q7

Secondary 4
8 marks
  1. Two variables \(x\) and \(y\) are related by the equation \(xy^2=ax+by\). Explain how a straight line graph can be drawn to represent the given equation.[2]
  2. The table shows experimental values of two variables \(x\) and \(y\). It is known that \(x\) and \(y\) are related by the equation \(y=p\mathrm{e}^{-qx}\) where \(p\) and \(q\) are constants.

    \(x\)

    \(1\)

    \(3\)

    \(5\)

    \(7\)

    \(9\)

    \(y\)

    \(98.2\)

    \(65.9\)

    \(44.1\)

    \(29.6\)

    \(19.8\)

    1. On the grid below plot \(\ln y\) against \(x\) and draw a straight line graph.[2]
    2. Use your graph to estimate
      1. the value of \(p\) and of \(q\),[3]
      2. the value of \(y\) when \(x=2\).[1]

Solution:

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Answer:(a) Plot \(y^2\) against \(y/x\); gradient \(b\), intercept \(a\). (b)(i) See plotted graph. (b)(ii)(a) \(p\approx120,\ q\approx0.200\). (b)(ii)(b) \(y\approx80.6\), depending on the fitted line.

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