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The slope of a line measures how steep the line is. [1] Being able to find the slope of a line, or using the slope to find points on the line, is an important skill used in economics, [2] geoscience, [3] accounting/finance and other fields.

Finding the Slope Intercept

  1. Find two points on the graph line in (x, y) format.
  2. Find the rise by counting points between the y-coordinates.
  3. Find the run by counting points between the x-coordinates from left to right.
  4. Place the rise over run in ratio form to find the slope.
Method 1
Method 1 of 4:

Using a Graph to Find the Slope

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  1. Draw dots on the graph to represent these points, and note their coordinates.
    • Remember when graphing points to list the x-coordinate first, then the y-coordinate.
    • For example, you might choose the points (-3, -2) and (5, 4).
  2. To do this, you must compare the difference in y of the two points. Begin with the first point, the point that is the farthest left on the graph, and count up until you reach the y-coordinate of the second point.
    • The rise can be positive or negative; that is, you can count up or down to find it. [4] If the line is moving up and to the right, the rise is positive. If the line is moving down and to the right, the rise is negative. [5]
    • For example, if the y-coordinate of the first point is (-2), and the y-coordinate of the second point is (4), you will count up 6 points, so your rise is 6.
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  3. To do this, you must compare the difference in x of the two points. Begin with the first point, the point that is farthest left on the graph, and count over until you reach the x-coordinate of the second point.
    • To run is always positive; that is, you can only count from left to right, never right to left. [6]
    • For example, if the x-coordinate of the first point is (-3), and the x-coordinate of the second point is (5), you will count over 8, so your run is 8.
  4. The slope is usually in fraction form, but it can also be a whole number.
    • For example, if the rise is 6 and the run is 8, then your slope is , which can be simplified to .
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Method 2
Method 2 of 4:

Using Two Given Points to Find the Slope

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  1. Set up the formula . In the formula, m = the slope, = the coordinates of the first point, = the coordinates of the second point.
    • Remember that the slope is equal to . You are using this formula to find the change in y (rise) over the change in x (run). [7]
  2. Make sure you place the coordinates of the first point ( ) and the second point ( ) in the correct positions in the formula, or else you will not calculate the correct slope.
    • For example, given the points (-3, -2) and (5, 4), your formula will look like this: .
  3. This will give you the slope as a fraction or whole number.
    • For example, if your slope is you should calculate in the numerator (Remember when subtracting a negative number, you add.) and in the denominator. You can simplify to , so .
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Method 3
Method 3 of 4:

Finding the y-intercept, Given the Slope and One Point

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  1. In the formula, y = the y-coordinate of any point on the line, m = slope, x = the x-coordinate of any point on the line, and b = the y-intercept.
    • is the equation of a line. [8]
    • The y-intercept is the point at which the line crosses the y-axis.
    EXPERT TIP

    Grace Imson, MA

    Math Instructor, City College of San Francisco
    Grace Imson is a math teacher with over 40 years of teaching experience. Grace is currently a math instructor at the City College of San Francisco and was previously in the Math Department at Saint Louis University. She has taught math at the elementary, middle, high school, and college levels. She has an MA in Education, specializing in Administration and Supervision from Saint Louis University.
    Grace Imson, MA
    Math Instructor, City College of San Francisco

    Our Expert Agrees: If you have the slope and one point, plug them into the equation of the line. In y = mx + b, m is the slope, and the point coordinate will contain both x and y. Then, solve for b to find the y-intercept.

  2. Remember, the slope is equal to the rise over the run. If you need help finding the slope, see the instructions above.
    • For example, if the slope is , and on point on the line is (5,4), then the formula will look like this: .
  3. First multiply the slope and the x-coordinate. Subtract this number from both sides to solve for b.
    • In the example problem the equation becomes . Subtracting from both sides, you end up with . So the y-intercept is .
  4. On a coordinate graph, plot your known point, then draw a line using the slope. To find the y-intercept, look for the point where the line crosses the y-axis.
    • For example, if the slope is , and one point is (5,4), draw a point at (5,4), then draw other points along the line by counting to the left 4 and down 3. When you draw a line through the points, you should see the line cross the y-axis just above the (0,0) coordinate.
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Method 4
Method 4 of 4:

Finding the x-intercept, Given the Slope and Y-intercept

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  1. In the formula, y = the y-coordinate of any point on the line, m = slope, x = the x-coordinate of any point on the line, and b = the y-intercept.
    • is the equation of a line. [9]
    • The x-intercept is the point at which the line crosses the x-axis.
  2. Remember, the slope is equal to the rise over the run. If you need help finding the slope, see the instructions above.
    • For example, if the slope is , and the y-intercept is , the formula will look like this: .
  3. [10] You are looking for the x-intercept, the point at which the line crosses the x-axis. At this point, the y-coordinate will equal zero. So if we set y to 0, and solve for the corresponding x-coordinate, we will find the point (x, 0), which will be the x-intercept.
    • In the example problem, the equation becomes .
  4. First subtract the y-intercept from both sides. Then divide both sides by the slope.
    • In the example problem the equation becomes . Dividing both sides by , you end up with . This simplifies to . So the point at which the line crosses the x-axis is . So the x-intercept is .
  5. On a coordinate graph, plot your y-intercept, then draw a line using the slope. To find the x-intercept, look for the point where the line crosses the x-axis.
    • For example, if the slope is , and the y-intercept is , draw a point at , then draw other points along the line by counting to the left 4 and down 3, and to the right 3 and up 4. When you draw a line through the points, you should see the line cross the x-axis just left of the (0,0) coordinate.
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Community Q&A

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  • Question
    How do I write an equation for the line with a slope of 6 and y-intercept of -3?
    Donagan
    Top Answerer
    Use the formula y = mx + b, where m is the slope and b is the y-intercept.
  • Question
    How do I write the equation of a line, given the slope and y-intercept?
    Donagan
    Top Answerer
    Assuming you're talking about a linear (straight-line) equation, you would use the standard slope/y-intercept form, y = mx + b. Use the given slope for m, the coefficient of x. Use the given y-intercept for b, the constant in the equation. For example, if the slope is 3 and the y-intercept is -5, the equation would be y = mx + b = 3x + (-5) = 3x - 5.
  • Question
    What is intercept and how do I calculate this using a graph?
    Community Answer
    There are two types of intercept, x-intercept and y-intercept. When we say x-intercept, this means the line passes through the x-axis with coordinates (x,0). When we say y-intercept, the graph passes through the y-axis with coordinates (0,y). To find x or y intercepts, just observe where the line on the graph cuts the x or y axis respectively.
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      About This Article

      Article Summary X

      To find the slope of a line from a graph, first choose 2 points along the line and write down the X and Y coordinates for each. Next, find the rise by taking the difference between the 2 Y coordinates. If the line slopes up as it moves to the right, the rise will be positive. If it slopes down, the rise will be negative. Once you’ve found the rise, calculate the run by finding the difference between the 2 X coordinates, going from left to right. Finally, find the slope by dividing the rise by the run. Keep reading for more tips, including how to find the Y-intercept using the slope and 1 point!

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