2023 NJC P2 Q3

2023 NJC P2 Q3

8 marks
Prelims
  1. Using integration by parts on \(\displaystyle\displaystyle \displaystyle\int{\frac{{{\left( \ln x \right)}^{2}}}{{{x}^{2}}}}\mathrm{d}x\), show that
    \(\displaystyle\displaystyle \displaystyle\int{\frac{2\ln x}{{{x}^{2}}}\mathrm{d}x-}\displaystyle\displaystyle \displaystyle\int{\frac{{{\left( \ln x \right)}^{2}}}{{{x}^{2}}}\mathrm{d}x}=\frac{{{\left( \ln x \right)}^{2}}}{x}+c\),
    where \(c\) is an arbitrary constant.[3]
  2. Region \(~R\) is bounded by the curves \(y=\frac{\sqrt{2\ln x}}{x}\) and \(y=\frac{\ln x}{x}\). Find the exact volume generated by rotating \(~R\) about the \(x\)-axis through \(2\pi \) radians.[5]

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Answer:(a) \(\int\dfrac{2\ln x}{x^2}\,\mathrm dx-\int\dfrac{(\ln x)^2}{x^2}\,\mathrm dx=\dfrac{(\ln x)^2}{x}+c\) (b) \(\dfrac{4\pi}{e^2}\text{ units}^3\)

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