2015 NJC Promo Q6

2015 NJC Promo Q6

9 marks
Promo

The diagram shows the curves with equations \(y={{\mathrm{e}}^{2x-5}}\) and \(y={{\mathrm{e}}^{-3x}}\).

The shaded region \(R\) is bounded by the curves and the line \(x=2\).

  1. Find the \(x\)-coordinate of the point of intersection of the curves.[1]
  2. Find the exact area of \(R\), giving your answer in the form \(\frac{a}{\mathrm{e}}+\frac{b}{{{\mathrm{e}}^{3}}}+\frac{c}{{{\mathrm{e}}^{6}}}\), where \(a\), \(b\) and \(c\) are constants to be determined.[4]
  3. Find the numerical value of the volume of revolution formed when \(R\) is completely rotated about the \(y\)-axis.[4]

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Answer:(i) \(x=1\) (ii) Area \(=\dfrac1{2e}-\dfrac5{6e^3}+\dfrac1{3e^6}\), \(a=\dfrac12\), \(b=-\dfrac56\), \(c=\dfrac13\) (iii) \(1.53\text{ units}^3\) to \(3\) s.f.

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