2025 VJC Promo Q5

2025 VJC Promo Q5

Junior College 1
7 marks

It is given that \(\mathrm{f}(x)=\frac{e^x}{1+2e^x}\).

  1. Write down \(\int \mathrm{f}(x)\,dx\).[1]
  2. Using standard series from the List of Formulae (MF27), find the Maclaurin series for \(\mathrm{f}(x)\), up to and including the term in \(x^2\).[4]
  3. Hence, or otherwise, find the first four non-zero terms of the Maclaurin series for \(\ln(1+2e^x)\).[2]

Solution:

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Answer:\(\int \mathrm{f}(x)dx=\dfrac12\ln(1+2e^x)+C\); \(\mathrm{f}(x)=\dfrac13+\dfrac19x-\dfrac1{54}x^2+\cdots\); \(\ln(1+2e^x)=\ln3+\dfrac23x+\dfrac19x^2-\dfrac1{81}x^3+\cdots\)

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