Main content

## Algebra 1

### Unit 4: Lesson 2

Slope- Intro to slope
- Positive & negative slope
- Worked example: slope from graph
- Slope from graph
- Graphing a line given point and slope
- Graphing from slope
- Calculating slope from tables
- Slope in a table
- Worked example: slope from two points
- Slope from two points
- Slope review

© 2023 Khan AcademyTerms of usePrivacy PolicyCookie Notice

# Slope review

CCSS.Math: , , ,

The slope of a line is a measure of its steepness. Mathematically, slope is calculated as "rise over run" (change in y divided by change in x).

## What is slope?

Slope is a measure of the steepness of a line.

*Want an in-depth introduction to slope? Check out this video.*

### Example: Slope from graph

We're given the graph of a line and asked to find its slope.

The line appears to go through the points left parenthesis, 0, comma, 5, right parenthesis and left parenthesis, 4, comma, 2, right parenthesis.

In other words, for every three units we move vertically down the line, we move four units horizontally to the right.

*Want to learn more about finding slope from graphs? Check out this video.*

### Example: Slope from two points

We're told that a certain linear equation has the following two solutions:

Solution: x, equals, 11, point, 4, space, space, space, y, equals, 11, point, 5

Solution: x, equals, 12, point, 7, space, space, space, y, equals, 15, point, 4

And we're asked to find the slope of the graph of that equation.

The first thing to realize is that each solution is a point on the line. So, all we need to do is find the slope of the line through the points left parenthesis, 11, point, 4, comma, 11, point, 5, right parenthesis and left parenthesis, 12, point, 7, comma, 15, point, 4, right parenthesis.

The slope of the line is 3.

*Want to learn more about finding slope from two points? Check out this video.*

## Practice

*Want more practice? Check out this Slope from graphs exercise and this Slope from points exercise.*

## Want to join the conversation?

- I dont understand this slope thing at all

can you help me(3 votes)- You can always figure out the slope of a line if you have 2 points. If you are not given 2 points, you can find 2 points on the graph and use them to find the slope.

Here are some good things to know:

-**m**= slope

- (x₁, y₁) = point 1

- (x₂, y₂) = point 2

-**rise**= the difference in the y-values (y₂ - y₁)

-**run**= the difference in the x-values (x₂ - x₁)

In the**slope formula**, the slope (m) is equal to rise over run:

m = rise / run

= (y₂ - y₁) / (x₂ - x₁)

Let's say we are given a line with points (4, 2) and (6, 1). If we say that point 1 is (4, 2) and point 2 is (6, 1), then:

x₁ = 4 and x₂ = 6

y₁ = 2 and y₂ = 1

Now we just need to plug these values into the slope formula:

m = rise / run

= (y₂ - y₁) / (x₂ - x₁)

= (1 - 2) / (6 - 4)

= (-1) / 2

= -1/2

So the slope (m) is -1/2.

The main thing to keep track of is which point is (x₁, y₁) and which point is (x₂, y₂). You don't want to mix these up.

A few tips for graphs of slopes:

- a perfectly*horizontal*line has**no slope**

- a perfectly*vertical*line has a slope that is**not defined**

- a line that goes*upwards*(from left to right) has a**positive**slope

- a line that goes*downwards*(from left to right) has a**negative**slope

Hope this helps!(58 votes)

- why would you have to do the close one said it passes throw 0,5 and 4,2 why can't you just do it were it passes throw the x and y(16 votes)
- You can calculate the slope from the x- and y-intercepts. But in this case, we can't tell
*exactly*what the x-intercept is just from looking at the graph - we can only see that it is somewhere between 6 and 7.

In order to accurately calculate the slope, we need to use points where we know the exact value. We know the exact value of every point on the grid where the graph lines intersect. So when the line crosses one of those points, we know the exact coordinates for that point on the line.

For example:

(-4, 8)

(0, 5)

(4, 2)

(8, -1)

Any of these points may be used to calculate the slope, and you should get the same answer no matter which 2 points you use.

Hope this helps!(15 votes)

- Are you supposed to simplify 4.5 by 1.5??(3 votes)
- for the sake of the equation make 4.5 into 45 and make 1.5 into 15. From here, simplify 45/15. once you are done simplifying, 45/15 into 3/1, you have to reverse it to make it into the correct answer for slope equations (difference of y/difference of x).(4 votes)

- This is confusing me?

Any helpp for the last question?(10 votes) - How can it be a fraction, because when I put in a number that we used in class, it said that what I put in was wrong. If you guys could explain that concept to me that would be greatly appreciated(11 votes)
- The slope of a line is defined as a fraction: rise over run; or (y2-y1)/(x2-x1). So slope is always a fraction. Even if you get a number like 5 as a slope, you need to change it into 5/1 (fraction form) to understand what it means related to the lines movement.(2 votes)

- I just don't understand.... how do you tell the slope?(10 votes)
- 1 coordinate will be x2,y2.(the 2's and 1's are just to show which coordinate is which not for multipying x)

Another will be x1,y1.

Do y2-y1 Divided by x2-x1.(2 votes)

- I was wondering if you only have lets say, 2 points on a line, and I was wondering if you could solve for the slope, even if thats all you have(5 votes)
- Two points would be enough.

Your points would be (x1, y1) and (x2, y2) then the slope m would be:

m = y1 - y2 / x1 - x2(13 votes)

- Is the slope y divide by x?(7 votes)
- Slope= y2-y1/x2-x1(2 votes)

- so all the x numbers go on the bottom and y goes on top(3 votes)
- I assume you mean if given any two points on the line, the two x values subtracted on bottom and the two y values subtracted on top which is correct(2 votes)

- I am confused on how to find the slope in an equation(3 votes)
- Since it is different than everything you have been doing so far, it is natural to be confused.

The slope is part of the equation of a line.

Y = mX + Y intercept

Is the equation you will see a lot.

The m represents the coefficient multiplied by X. Together, m and X are the slope.

Take two points on the line. Any two points that the line passes through.

(2,3) (0,1)

It is important to note you are*not*multiplying the numbers.

The 2 and 0 represent the x coordinate and the 3 and 1 represent the y coordinate.

To finish finding the slope, you take the 2nd y coordinate, in this case 1, and minus the 1st y coordinate from the 2nd.

This equals -2.

You then take the 2nd x coordinate and subtract the 1st x coordinate from the 2nd. This equals -2.

You divide the y value and by the x value. -2/-2 = 1

The slope is 1.

Y (subscript) 2 - Y (subscript) 1 / X (subscript) 2 - X (subscript) 1 = slope

Hope this helps.(2 votes)