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

Oct 6, 2014

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.

Feb 21, 2017

Slope is defined as $r i s e$ divided by $r u n$
A line parallel to the $y$ axis is a vertical line that has no $r u n$ so it defies the definition.
A line parallel to the $x$ axis has no $r i s e$ but it follows the definition because a slope of $0$ can be calculated.