A vertical line is a line that is parallel to the y-axis of the coordinate plane.
The general equation of a vertical line is x=c where c is a constant. The relation x=c means that the x-value or input value never changes or stays the same. But, the y-values of the ordered pairs of a vertical line can assume any values.
If we take any two points of a vertical line and find the slope, it will have an “infinite slope” which is sometimes referred to as undefined slope.
Example: Graph x=-1.
Since the value of x doesn’t change, we can describe at least five points or ordered pairs that lie on the vertical line, y=3 which can be (-1,4), (-1,3), (-1,2), (-1,1), and (-1,0). If we plot these points on the coordinate plane, we will get a vertical line.