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Slope of a line




 
Related Topics:
More Lessons for Geometry, Math Worksheets

In this lesson, we will learn
  • how to find the slope of a line from the graph using rise over run.
  • how to find the slope of a line using the slope formula.
  • how to find the y-intercept from the graph.

Slope of a line

The slant of a line is called the slope. Slope describes how steep a line is. The slope of a line can be found using the ratio of rise over run between any two points on the line.

slope

In the following graph, the rise from point P to point Q is 2 and the run from point P to point Q is 4.

slope

coord plane: slope

Take note that the slope obtained would be the same no matter which two points on the line were selected to determine the rise and the run.

A horizontal line has a slope of zero. A vertical line has an undefined slope.

A line with a positive slope slant upwards, whereas a line with a negative slope slant downwards.




This video shows how to find the slope of a line using the ratio of rise over run between any two points on the line
This video shows how to calculate the slope of a line using the rise over run method. It also explains positive slope, negative slope, and the slope of horizontal and vertical lines.



 

Slope Formula

Slope can also be calculated as the ratio of the change in the y-value over the change in the x-value.

Given any two points on a line, (x1, y1) and (x2, y2), we can calculate the slope of the line by using this formula:

slope formula

For example: Given two points, P = (0, –1) and Q = (4,1), on the line we can calculate the slope of the line.

    slope = change in y / change in x= slope values

Let's look at a line that has a negative slope.

For example: Consider the two points, R(–2, 3) and S(0, –1) on the line. What would be the slope of the line?

    slope = change in y / change in x = negative slope

This video shows how to find the slope of the line that passes through two points when given the coordinates of the points. To solve the problem (without graphing), we can use the slope formula, which states that m = (y2y1) / (x2x1). The slope formula can be read as "slope equals the second y-coordinate minus the first y-coordinate over the second x-coordinate minus the first x-coordinate".



This video gives three examples of how to use the slope formula to find the slope of a line given the coordinates of two points on the line. It shows that the slope can be zero or undefined.

Y-intercept

The y-intercept is where the line intercepts (meets) the y-axis.

In the following diagram, the line intercepts the y-axis at (0,–1). Its y-intercept is equal to –1.

negative slope

Equation of a straight line can be written in slope-intercept form.


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