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Centroid Of A Triangle

  1. Dec 9, 2014 #1
    1. The problem statement, all variables and given/known data
    Hello. In class we learned how to calculate centroids of a triangle. For the y-coordinate we use the formula height/3 and for the x we use 2/3 * base

    2. Relevant equations
    In the diagram, If I want to calculate the y coordinate , I do 72 (which is the proposed height)/ 3 ; only to get y=24 which is incorrect.

    It turns out that to find the y-coordinate in this case we must do 2/3*height. Why is that so? This is really confusing.
    Why did the formulas to calculating 'y' and 'x' values switch?

    Thank you for your time.
     

    Attached Files:

  2. jcsd
  3. Dec 9, 2014 #2

    Mark44

    Staff: Mentor

    Because the triangle is upside down. The "base" is at the top and you have to measure 1/3 of the way down.
     
  4. Dec 9, 2014 #3
    But the height is still 72? and one more thing, when we say the height do we automatically pick the longest side of the triangle?

    Edit: Okay I see what you mean now. If I do h/3 , I get 24 but that is from the top not the bottom of the plane.

    However, how would you calculate the x-coordinate?
     
    Last edited: Dec 9, 2014
  5. Dec 10, 2014 #4

    Mark44

    Staff: Mentor

    Usually, what we call the base is at the bottom and horizontal, and the altitude or height is the vertical distance from the base to the opposite vertex. This triangle is oriented so that the base is at the top. When you calculate the area using A = (1/2) b * h, any side can be considered the base.
    You have the formula in your first post.
     
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