Checking Parallelism with Direction Vectors

00:00 3 marks

  • Build Confidence
  • HL
  • Tier 2
  • Parallel lines
  • Direction vectors
  • Vector equations
  • scalar multiples

Given the line \(r: \vec{x} = \begin{pmatrix} 2 \\ -3 \end{pmatrix} + t\begin{pmatrix} 4 \\ 5 \end{pmatrix}\) and the line \(s: \vec{x} = \begin{pmatrix} -1 \\ 1 \end{pmatrix} + u\begin{pmatrix} -8 \\ -10 \end{pmatrix}\), determine if the two lines are parallel. Justify your answer by comparing their direction vectors.

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Hint

To check for parallelism, determine if the direction vector of line \(s\) is a scalar multiple of the direction vector of line \(r\).

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Complete Answer

The lines are parallel because the direction vector of line \(s\) is a scalar multiple of the direction vector of line \(r\), specifically \(\begin{pmatrix} -8 \\ -10 \end{pmatrix} = -2\begin{pmatrix} 4 \\ 5 \end{pmatrix}\).

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