Vectors - Perpendicular Projection and Reflection in a Plane

Vectors - Perpendicular Projection and Reflection in a Plane

8 marks

Referring to the origin \(O\), two planes \(\pi_1\) and \(\pi_2\) are given by

\[\pi_1 : \mathbf{r} \cdot \begin{pmatrix} 1 \\ 2 \\ 2 \end{pmatrix} = 18 \quad \text{and} \quad \pi_2 : \mathbf{r} \cdot \begin{pmatrix} 2 \\ -1 \\ 2 \end{pmatrix} = 3.\]

  1. Given that point \(A(2, 5, 2)\) lies on \(\pi_2\), find \(\overrightarrow{OB}\), where \(B\) is the image of \(A\) when reflected in the plane \(\pi_1\).[4]
  2. Find a vector equation of the line of intersection of \(\pi_1\) and \(\pi_2\).[1]
  3. Find the Cartesian equation of the plane which is the image of \(\pi_2\) when \(\pi_2\) is reflected in \(\pi_1\).[3]

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Answer:(i) \(\overrightarrow{OB}=\dfrac19\begin{pmatrix}22\\53\\26\end{pmatrix}\) (ii) \(\mathbf r=\begin{pmatrix}0\\5\\4\end{pmatrix}+\mu\begin{pmatrix}6\\2\\-5\end{pmatrix},\ \mu\in\mathbb R\) (iii) \(10x-25y+2z=-117\)

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