Parallel & Perpendicular Lines
Parallel lines have the same gradient.
\(m_1 = m_2\)
Perpendicular lines have gradients that multiply to -1.
\(m_1 \times m_2 = -1 \)
Example
\(y = 2x + 1\) and \(y = 2x - 3\) are parallel (both gradients = 2)
\(y = \dfrac{1}{2}x\) and \(y = -2x\) are perpendicular (\(\dfrac{1}{2} \times -2 = -1\))
Practice
Which is perpendicular to \(y = 3x + 1\)?
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