Question

What is the slope of a line parallel to the y-axis?

Answer 1

Parallel lines have the same slope.

Vertical lines have an undefined slope.

The `y`-axis is a vertical.

A line that is parallel to the `y`-axis also has to be vertical.

The slope of a line parallel to the `y`-axis has a slope that is undefined.

Answer 2

A line parallel to the y-axis - a.k.a. vertical line has no slope!

Explanation:

Slope is defined as `rise` divided by `run`

A line parallel to the `y` axis is a vertical line that has no `run` so it defies the definition.

A line parallel to the `x` axis has no `rise` but it follows the definition because a slope of `0` can be calculated.