# Planar Orthogonality

Suppose we have two lines, $$y_1$$ and $$y_2$$, defined by,

$y_1 \equiv m_1 x_1 + b_1\,\text{ and,}$ $y_2 \equiv m_2 x_2 + b_2$

If the two lines are orthogonal, then,

$m_1 \cdot m_2 = -1$