Rational Trigonometry/13

Angles are not as good as spreads. Angles cannot be typically calculated with anything but approximations. Spreads are not so.

Suppose we have two lines through the origin with equals


 * Ax + By = 0
 * Cx + Dy = 0

Then the spread between them is

$$s = \frac{(AD-CB)^2}{(A^2+B^2)(C^2+D^2)} $$