Horizontal lines run left to right, parallel to the horizon, with slope 0 and equation y = k. Vertical lines run top to bottom, perpendicular to the horizon, with undefined slope and equation x = k.

Higher - The gradients of two perpendicular lines will always multiply to make –1. Make sure you are familiar with finding the equation of a line and calculating gradient to understand equations of ...

Learn how to write the equation of a line that is perpendicular to a given line. The equation of a line is such that its highest exponent on its variable(s) is 1. (i.e. there are no exponents in its ...