Chapter 2 - Graphs and Functions - 2.5 Equations of Lines and Linear Models - 2.5 Exercises - Page 242: 3

$x$

RECALL: A vertical line has an equation in the form $x=h$ where $h$ is a real number. All points on the line have an x-coordinate of $h$. The given vertical line contains the point $(-4, 8)$. The x-coordinate of this point is $-4$. Thus, the equation of the vertical line is $x=-4$. Therefore, the missing expression in the given statement is: $x$