# How do you find the slope that is perpendicular to the line  x = 4?

Sep 7, 2017

You know that $x = 4$ represents a vertical line passing through point $x = 4 , y = 0$:
we can think that the perpendicular, in the form $y = m x + c$, must be perfectly horizontal, i.e., have a slope:
$m = 0$
giving a line of equation $y = c$ where $c$ will be a real number (for example $y = 3$):