Slope

The slope is different depending on whether the line is Horizontal or Vertical. If a line is vertical, then the slope would be undefined and go straight up and down forever. However, if the line is horizontal then the it is called a Zero/0 slope and goes left and right forever.

All vertical lines share the same slope no matter what, this also goes for horizontal lines

Function/Not A Function

Whether is slope is a function, again depends on if it is vertical or horizontal. For example, if you apply the vertical line test to an vertical line it will touch on multiple points (every point possible) making it not a function.

If you were to apply the vertical line test to a horizontal line or zero slope it would only touch on a single point, making horizontal lines a function. If you were to then go apply the horizontal line test, as the line is also horizontal it would touch on multiple (every) point, making it not a 1 to 1 function

Domain and Range

The domain and range on vertical and horizontal lines is pretty simple. In a horizontal line, the domain is only a single number. Although in a vertical line the range is only a single number.

E.X. (0,1) (0,2) (0,3) is a horizontal line/zero slope. (1,0) (2,0) (3,0) is a vertical line/undefined slope.

Equation

The equations for vertical and horizontal lines are quite short, but can be easy to mix up. The equation for a horizontal line for example would be Y=2, this is the equation because two is the Y intercept, and all points will be on the Y value of two.

It is the opposite for vertical lines. For example for a vertical line it would be X=2, two being the X intercept and all good points would be on the X value of two.