## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$x=3$
If the slope is undefined, we can surely state that the line is vertical. The equation of a vertical line is always in the form of: $x=a$, where $a$ is constant. Here, the point given is $(3,8)$, which is on the line. For this point, $x=3$ and this should be true for the other points on the line. The equation is, therefore: $x=3$