Horizontal lines in the coordinate plane represent situations where the -value doesn’t change at all while the -value changes.

The horizontal line that goes through the point can be described by saying that “for all points on the line, the -value is always 3.” Since horizontal lines are neither increasing or decreasing, they have a slope of 0, and so an equation for this horizontal line is , or just .

Vertical lines in the coordinate plane represent situations where the -value doesn’t change at all while the -value changes.

The vertical line that goes through the point can be described by saying that “for all points on the line, the -value is always -2.” An equation that says the same thing is .