2006 HCI P1 Q14

2006 HCI P1 Q14

In the diagram, \(O\) is the centre of the rectangular base \(ABCD\) of a right pyramid with vertex \(V\). Perpendicular unit vectors \(\mathbf{i}\), \(\mathbf{j}\), \(\mathbf{k}\) are parallel to \(AB\), \(BC\) and \(OV\) respectively. The length of \(AB\), \(BC\) and \(OV\) are \(12\text{ cm}\), \(6\text{ cm}\) and \(6\text{ cm}\) respectively. A line \(l\) has Cartesian equation \(\frac{-x-4}{10} = y+2 = \frac{t-z}{-2}.\)

  1. Find a vector equation of \(AV\).
  2. If the line \(l\) intersects \(AV\) at \(M\), find the position vector of \(M\) and the value of \(t\).
  3. Find the acute angle between \(AV\) and the line \(l\). Hence find the perpendicular distance from \(A\) to the line \(l\).

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Answer:(i) \(\mathbf r=\begin{pmatrix}0\\0\\6\end{pmatrix}+\lambda\begin{pmatrix}2\\1\\2\end{pmatrix}\) (ii) \(\overrightarrow{OM}=\begin{pmatrix}-4\\-2\\2\end{pmatrix}\), \(t=2\) (iii) \(60.8^\circ\), \(2.62\) cm

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