# How do you write an equation that contains points (5, 1) and is perpendicular to y=3?

$x = 5$
$y = 3$ is a horizontal line
Any line perpendicular to it must be a vertical line (that is it must be of the form $x = c$ for some constant $c$)
If such a line goes through $\left(5 , 1\right)$ it must be
$\textcolor{w h i t e}{\text{XXX}} x = 5$