What is the equation of a vertical line passing through x = 4?

A vertical line is defined by a constant value of x, meaning that regardless of the value of y, x remains constant. In this case, the line passes through the point where x equals 4. Therefore, the equation that represents this vertical line is simply the statement that x is always equal to 4.

The choice x = 4 correctly captures this idea, indicating that for any point on this line, the x-coordinate will always be 4. Since vertical lines do not have a specific value for y (it can be any real number), the line extends infinitely in the vertical direction, correlating to all possible y-values while keeping x fixed at 4.

This is why the equation x = 4 accurately represents the vertical line you are looking for. Other choices either represent horizontal lines or lines that are not related to the specified vertical line.