How to Find the Midpoint of a Line Segment

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Finding the midpoint of a line segment is easy as long as you know the coordinates of the two endpoints. The most common way to do this is to use the midpoint formula, but there's another way to find the midpoint of a line segment if it's vertical or horizontal. If you want to know how to find the midpoint of a line segment in just a few minutes, just follow these steps.

Method 1
Method 1 of 2:

Use the Midpoint Formula

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  1. The midpoint of a line segment is the point that is located on the exact midpoint of the two endpoints. Therefore, it's the average of the two endpoints, which is the average of the two x-coordinates and the two y-coordinates. [1]
  2. The midpoint formula can be used by adding the x-coordinates of the two endpoints and dividing the result by two and then adding the y-coordinates of the endpoints and dividing them by two. [2] This is how you will find the average of the x and y coordinates of the endpoints. [3] This is the formula: [(x 1 + x 2 )/2,( y 1 + y 2 )/2]
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  3. You can't use the midpoint formula without knowing the x and y-coordinates of the endpoints. In this example, you want to find the midpoint, point O, which is between the two endpoints M (5,4) and N (3,-4). Therefore, (x 1 , y 1 ) = (5, 4) and (x 2 , y 2 ) = (3, -4). [4]
    • Note that either pair of coordinates can serve as (x 1 , y 1 ) or (x 2 , y 2 ) -- since you'll just be adding the coordinates and dividing by two, it doesn't matter which pair is first.
  4. Now that you know the coordinates of the endpoints, you can plug them into the formula. Here's how you do it: [5]
    • [(5 + 3)/2, (4 + -4)/2]
  5. Once you've plugged the appropriate coordinates into the formula, all you have to do is the simple arithmetic that will give you the midpoint of the two line segments. [6] Here's how you do it:
    • [(5 + 3)/2, (4 + -4)/2] =
    • [(8/2), (0/2)] =
    • (4, 0)
    • The midpoint of the endpoints (5,4) and (3, -4) is (4,0).
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Method 2
Method 2 of 2:

Find the Midpoint of Vertical or Horizontal Lines

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  1. Before you can use this method, you'll need to know how to locate a vertical or horizontal line. [7] Here's how to spot it:
    • A line is horizontal if the two y-coordinates of the endpoints are equal. For example, the line segment with the endpoints (-3, 4) and (5, 4) is horizontal.
    • A line is vertical if the two x-coordinates of the endpoints are equal. For example, the line segment with the endpoints (2, 0) and (2, 3) is vertical.
  2. You can easily find the length of the segment just by counting how many horizontal spaces it takes up if it's horizontal, and counting how many vertical spaces it takes up if it's vertical. Here's how to do it: [8]
    • The horizontal line segment with the end points (-3, 4) and (5, 4) is 8 units long. You can find this by counting the spaces it takes up or by adding the absolute values of the x-coordinates: |-3| + |5| = 8
    • The vertical line segment with the end points (2, 0) and (2, 3) is 3 units long. You can find this by counting the spaces it takes up or by adding the absolute values of the y-coordinates: |0| + |3| = 3
  3. Now that you know the length of the line segment, you can divide it by two. [9]
    • 8/2 = 4
    • 3/2 = 1.5
  4. This is the last step to finding the endpoint of the line segment. Here's how you do it: [10]
    • To find the midpoint of the points (-3, 4) and (5, 4), just shift over 4 units either from the left or right to reach the middle of the segment. (-3, 4) shifted over 4 x-coordinates is (1, 4). You won't need to change the y-coordinates since you know the midpoint will be on the same y-coordinate as the endpoints. The midpoint of (-3, 4) and (5, 4) is (1, 4).
    • To find the midpoint of the points (2, 0) and (2, 3), just shift over 1.5 units either from the top or bottom to reach the middle of the segment. (2, 0) shifted up 1.5 y-coordinates is (2, 1.5). You won't need to change the x-coordinates since you know the midpoint will be on the same x-coordinate as the endpoints. The midpoint of (2, 0) and (2, 3) is (2, 1.5).
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  • Question
    How do I find the other end of the line segment if I'm given one end and the midpoint?
    Donagan
    Top Answerer
    The line segment extends beyond the midpoint a distance equal to the distance between the given end point and the midpoint. As a simple example, if the line segment begins at (0,0) and has a midpoint at (2,3), the line segment extends 2 x-units and 3 y-units beyond (2,3), meaning that the line segment ends at (4,6).
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  • Question
    How do I find the point that is one forth of the way from (2,4) to (10,8)?
    Donagan
    Top Answerer
    Solve this by inspection: the point's x-coordinate is one-quarter of the way from 2 to 10, which is 4. The point's y-coordinate is one-quarter of the way from 4 to 8, which is 5. Thus, the point's coordinates are (4,5).
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  • Question
    What is the midpoint of a line segment with endpoint at (0,8) and (-8,0)?
    Donagan
    Top Answerer
    As shown in the above article, the midpoint's x-coordinate is halfway between the x-coordinates of the endpoints, 0 and -8 (i.e., -4), and the midpoint's y-coordinate is halfway between the y-coordinates of the endpoints, 8 and 0 (i.e., 4) Thus, the midpoint is located at (-4,4).
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      References

      1. ↑ http://www.mathopenref.com/midpoint.html
      2. ↑ https://www.purplemath.com/modules/midpoint.htm
      3. ↑ http://www.mathplanet.com/education/algebra-1/radical-expressions/the-distance-and-midpoint-formulas
      4. ↑ https://mathbitsnotebook.com/Geometry/CoordinateGeometry/CGmidpoint.html
      5. ↑ https://www.mathsisfun.com/algebra/line-midpoint.html
      6. ↑ https://www.khanacademy.org/math/geometry/hs-geo-analytic-geometry/hs-geo-distance-and-midpoints/v/midpoint-formula
      7. ↑ https://mathbitsnotebook.com/Geometry/CoordinateGeometry/CGmidpoint.html
      8. ↑ https://www.khanacademy.org/math/geometry-home/geometry-lines/basic-geo-measuring-segments/v/measuring-segments
      9. ↑ https://www.calculatorsoup.com/calculators/geometry-plane/midpoint-calculator.php
      1. ↑ https://www.chilimath.com/lessons/intermediate-algebra/midpoint-formula/

      About This Article

      Article Summary X

      In order to find the midpoint of a line segment, you first have to understand that it’s the point located on the exact midpoint of the 2 endpoints, so it’s the average of the endpoints. To use the midpoint formula, add the x-coordinates of the endpoints and divide the result by 2. Then, add the y-coordinates of the endpoints and divide them by 2. Once you know the coordinates of the endpoints, you can plug them into the formula and solve. To learn how to find the midpoint of the vertical and horizontal lines, keep reading!

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