The idea of slope is something you encounter often in everyday life. Think about rolling a cart down a ramp or climbing a set of stairs. Both the ramp and the stairs have a slope. You can describe the slope, or steepness, of the ramp and stairs by considering horizontal and vertical movement along them. In conversation, you use words like “gradual” or “steep” to describe slope. Along a gradual slope, most of the movement is horizontal. Along a steep slope, the vertical movement is greater.
You are watching: What is the slope of the line shown below?
The mathematical definition of The ratio of the vertical change to the horizontal change of two points on a line.
")">slope is very similar to our everyday one. In math, slope is used to describe the steepness and direction of lines. By just looking at the graph of a line, you can learn some things about its slope, especially relative to other lines graphed on the same coordinate plane. Consider the graphs of the three lines shown below:
First, let’s look at lines A and B. If you imagined these lines to be hills, you would say that line B is steeper than line A. Line B has a greater slope than line A.
Next, notice that lines A and B slant up as you move from left to right. We say these two lines have a positive slope. Line C slants down from left to right. Line C has a negative slope. Using two of the points on the line, you can find the slope of the line by finding the rise and the run. The vertical change between two points is called the rise, and the horizontal change is called the run. The slope equals the rise divided by the run:
.Finding the Slope of a Line from a Graph
You can determine the slope of a line from its graph by looking at the rise and run. One characteristic of a line is that its slope is constant all the way along it. So, you can choose any 2 points along the graph of the line to figure out the slope. Let’s look at an example.
Example  
Problem  Use the graph to find the slope of the line.
 
 rise = 2  Start from a point on the line, such as (2, 1) and move vertically until in line with another point on the line, such as (6, 3). The rise is 2 units. It is positive as you moved up. 
run = 4  Next, move horizontally to the point (6, 3). Count the number of units. The run is 4 units. It is positive as you moved to the right.  
Slope =  Slope = .  
Answer  The slope is . 
This line will have a slope of no matter which two points you pick on the line. Try measuring the slope from the origin, (0, 0), to the point (6, 3). You will find that the rise = 3 and the run = 6. The slope is
. It is the same!Let’s look at another example.
Example  
Problem  Use the graph to find the slope of the two lines.

 
 Notice that both of these lines have positive slopes, so you expect your answers to be positive.  
 rise = 4  Blue line Start with the blue line, going from point (2, 1) to point (1, 5). This line has a rise of 4 units up, so it is positive.  
run = 1  Run is 1 unit to the right, so it is positive.  
Slope =  Substitute the values for the rise and run in the formula Slope = .  
rise = 1  Red line The red line, going from point (1, 2) to point (3, 1) has a rise of 1 unit.  
run = 4  The red line has a run of 4 units.  
Slope =  Substitute the values for the rise and run into the formula Slope =.  
Answer  The slope of the blue line is 4 and the slope of the red line is .  
When you look at the two lines, you can see that the blue line is steeper than the red line. It makes sense the value of the slope of the blue line, 4, is greater than the value of the slope of the red line,
. The greater the slope, the steeper the line.The next example shows a line with a negative slope.
Example  
Problem  Find the slope of the line graphed below.
 
 rise = −3  Start at Point A, (0, 4) and rise −3. This means moving 3 units in a negative direction. 
run = 2  From there, run 2 units in a positive direction to Point B (2, 1).  
Slope =  Slope = .  
Answer  The slope of the line is . 
Direction is important when it comes to determining slope. It’s important to pay attention to whether you are moving up, down, left, or right; that is, if you are moving in a positive or negative direction. If you go up to get to your second point, the rise is positive. If you go down to get to your second point, the rise is negative. If you go right to get to your second point, the run is positive. If you go left to get to your second point, the run is negative. In the example above, you could have found the slope by starting at point B, running −2, and then rising +3 to arrive at point A. The result is still a slope of
. Advanced Example  
Problem  Find the slope of the line graphed below.  
rise = 4.5  Start at (3, 0.25) and rise 4.5. This means moving 4.5 units in a positive direction.  
run = 6  From there, run 6 units in a positive direction to (3, 4.25).  
Answer  The slope of the line is 0.75.  
Looking at Equations
The slope of a line can sometimes be quickly determined from its equation. Let’s consider the line whose equation is y = 5x. You can create a table of values to find 3 points on the line.
x  y 
−1  −5 
0  0 
2  10 
Plotting these points, create the graph of the line and determine the slope.
As you move from the point (1, 5) to the point (2, 10), the line has a rise of 15 and a run of 3, so the slope of the line is
. Notice that the number 5 also appears in the equation: y = 5x.Whenever the equation of a line is written in the form y = mx + b, it is called the slopeintercept form of the equation. The m is the slope of the line. And b is the b in the point that is the yintercept (0, b).
For example, for the equation y = 3x – 7, the slope is 3, and the yintercept is (0, −7).
What if the equation is written as 2y = 5x + 1? Then you must rewrite the equation in the form y = mx + b. Solve for y.
2y = 5x + 1
y =
divide both sides of the equation by 2.The slope is
, and the yintercept is (0, ). What is the slope of the line whose equation is y = −2x + 7? A) 7 B) 2 C) −2 D) Show/Hide Answer A) 7 Incorrect. The slope for a line written in y = mx + b is given by the coefficient of x. The correct answer is −2. B) 2 Incorrect. The slope for a line written in y = mx + b is given by the coefficient of x. The coefficient is −2. The correct answer is −2. C) −2 Correct. The slope for a line written in y = mx + b is given by the coefficient of x. For this line the coefficient, or m, the slope, is −2. D) Incorrect. The slope for a line written in y = mx + b is given by the coefficient of x. The coefficient is −2. The correct answer is −2. Finding the Slope of a Line Given Two Points You’ve seen that you can find the slope of a line on a graph by measuring the rise and the run. You can also find the slope of a straight line without its graph if you know the coordinates of any two points on that line. Every point has a set of coordinates: an xvalue and a yvalue, written as an ordered pair (x, y). The x value tells you where a point is horizontally. The y value tells you where the point is vertically. Consider two points on a line—Point 1 and Point 2. Point 1 has coordinates (x1, y1) and Point 2 has coordinates (x2, y2). The rise is the vertical distance between the two points, which is the difference between their ycoordinates. That makes the rise y2 − y1. The run between these two points is the difference in the xcoordinates, or x2 − x1. So, or In the example below, you’ll see that the line has two points each indicated as an ordered pair. The point (0, 2) is indicated as Point 1, and (−2, 6) as Point 2. So you are going to move from Point 1 to Point 2. A triangle is drawn in above the line to help illustrate the rise and run. You can see from the graph that the rise going from Point 1 to Point 2 is 4, because you are moving 4 units in a positive direction (up). The run is −2, because you are then moving in a negative direction (left) 2 units. Using the slope formula, .You do not need the graph to find the slope. You can just use the coordinates, keeping careful track of which is Point 1 and which is Point 2. Let’s organize the information about the two points:
The slope, = . The slope of the line, m, is −2.It doesn’t matter which point is designated as Point 1 and which is Point 2. You could have called (−2, 6) Point 1, and (0, 2) Point 2. In that case, putting the coordinates into the slope formula produces the equation . Once again, the slope m = −2. That’s the same slope as before. The important thing is to be consistent when you subtract: you must always subtract in the same order y2 − y1 and x2 − x1.
The example below shows the solution when you reverse the order of the points, calling (5, 5) Point 1 and (4, 2) Point 2.
Notice that regardless of which ordered pair is named Point 1 and which is named Point 2, the slope is still 3.
