Vectors - Perpendicular Projection and Reflection in a Plane

Vectors - Perpendicular Projection and Reflection in a Plane

11 marks

The line \(l\) passes through \(A(3, 1, 4)\) and is parallel to \(2\mathbf{i} + \mathbf{j} + \mathbf{k}\).

  1. State the vector equation of \(l\).[1]

The plane \(p\) has equation

\[\mathbf{r} \cdot \begin{pmatrix} 2 \\ -1 \\ -1 \end{pmatrix} = 7.\]

  1. Find the acute angle between \(l\) and \(p\).[2]
  2. Find the point of intersection of \(l\) and \(p\).[2]
  3. Find the vector equation of the reflection of \(l\) in \(p\).[6]

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Answer:(i) \(\mathbf r=\begin{pmatrix}3\\1\\4\end{pmatrix}+\lambda\begin{pmatrix}2\\1\\1\end{pmatrix},\ \lambda\in\mathbb R\) (ii) \(19.5^\circ\) (iii) \((9,4,7)\) (iv) \(\mathbf r=\begin{pmatrix}9\\4\\7\end{pmatrix}+\mu\begin{pmatrix}2\\5\\5\end{pmatrix},\ \mu\in\mathbb R\)

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