2025 DHS P1 Q9

2025 DHS P1 Q9

12 marks

The point A has coordinates \((1,-2,4)\) and the plane \(\pi_1\) has the equation \(2x-y+2z=5\)

  1. Find the exact shortest distance between \(A\) and \(\pi_1\).[2]

The plane \(\pi_2\) has equation \(x+3y-az=3\), where \(a\) is a constant.

  1. Find the vector equation of line \(l\), which is the line of intersection of \(\pi_1\) and \(\pi_2\), in terms of \(a\).[4]

The plane \(\pi_3\) has equation \(bx-2y+4z=3\), where \(b\) is a constant.

  1. Show that \((a-6)(b-4)=0\) if \(l\) is parallel to \(\pi_3\).[2]
  2. State the conditions that \(a\) and \(b\) must follow for the three planes to form a triangular prism, where all the planes are non-parallel and they do not have any point in common. Justify your answer.[4]
Similar questions are unavailable for this question.
Answer:(a)\(\frac{7}{3}units\) (b)\(l :r=\begin{pmatrix}\frac{18}{7}\\ \frac{1}{7}\\0\end{pmatrix} + \lambda \begin{pmatrix} a-6\\2a+2\\7\end{pmatrix},\lambda\in\mathbb{R}\) \(\,\mathrm (\lambda=\frac{1}{7}\lambda')\) (d)a=6 and \(b\in\mathbb{R} ot{-\frac{2}{3},\frac{23}{8},4}\)

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