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Example

Finding the Slopes of x=8x = 8 and y=5y = -5

Determine the slope of each line by first identifying whether it is vertical or horizontal from its equation.

The equation x=8x = 8 contains only the variable xx, so its graph is a vertical line. Every point on this line has an x-coordinate of 88, meaning there is no horizontal change between any two points — the run is always 00. Because division by zero is undefined, the slope of x=8x = 8 is undefined.

The equation y=5y = -5 contains only the variable yy, so its graph is a horizontal line. Every point on this line has a y-coordinate of 5-5, meaning there is no vertical change between any two points — the rise is always 00. Substituting into the slope formula gives m=0run=0m = \frac{0}{\text{run}} = 0. The slope of y=5y = -5 is 00.

This example illustrates a quick identification strategy: if the equation has only xx, the line is vertical with an undefined slope; if it has only yy, the line is horizontal with a slope of 00.

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Updated 2026-04-21

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