In a standard coordinate plane, what is the equation of a vertical line?

The equation of a vertical line is represented by the format where x is equal to a constant value. This indicates that no matter what value y takes, the value of x remains the same. A vertical line travels straight up and down the coordinate plane without changing its x-coordinate, which confirms that it is described by x = a constant.

In contrast, other forms represent different types of relationships. For example, if y were equal to a constant, this would describe a horizontal line, where the y-coordinate remains fixed while x varies. The equation y = mx signifies a linear relationship with a slope (m), typically representing lines that can be sloped, either upward or downward, rather than vertical. Lastly, the equation x = y reflects a diagonal line where both coordinates are equal, which is not a vertical line. Hence, the only option that accurately describes a vertical line in a coordinate plane is x = a constant.