2023 ASRJC P1 Q8

2023 ASRJC P1 Q8

9 marks
Prelims

It is given that \(y=\frac{1}{3+\sin 2x}\).

  1. Show that \(\frac{{{\mathrm{d}}^{2}}y}{\mathrm{d}{{x}^{2}}}-4{{y}^{2}}\sin 2x+4y\frac{\mathrm{d}y}{\mathrm{d}x}\cos 2x=0\). Hence find the Maclaurin series for \(y\), up to and including the term in \({{x}^{2}}\).[4]
  2. Given further that \(x\) is small so that \({{x}^{3}}\) and higher powers of \(x\) can be neglected, use appropriate expansions from the List of Formulae (MF26) to verify the correctness of the series of \(y\) in part (a).

    [3]
  3. Use the series expansion found in part (a) and integration to find an approximate value for \(\int_0^{1.5} \frac{1}{3+\sin 2x}\mathrm{d}x.\).

    [2]

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Answer:(a) \({\frac{1}{3} - \frac{2}{9}x + \frac{4}{27}x^2}\) (c) \({\frac{5}{12}}\) or \({0.417}\)

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