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Teaching Guides

## Calculating the Slope of a Line

Posted by scott-locklear on September 11, 2013

The slope of a line or line segment is the value that describes its steepness, incline, or grade. Think of a skier or snowboarder going down a ski slope. The steeper the hill, the higher the value of the slope will be.

Key Points

• You’ll need to know the coordinates of two points on a line to calculate its slope.
• The slope of a horizontal line is zero because a horizontal line has no rise.
• The slope of a vertical line is undefined because change in x (Δx) is zero, and you can’t divide by zero.
• A line with a slope that goes up as it goes to the right on a graph will have a positive slope, while one that goes down to the right will have a negative slope. One of the most common mistakes when calculating slope is to miss or add an extra negative sign when working the formula, so take a quick look at your graph (or make one if you weren’t given one!) when you’re done and make sure the line agrees with your calculation.
• Slope is often expressed as the letter “m” in the full equation of a line, which you will often use when calculating the y-intercept.

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