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Sloving triangles in 3d

  1. Sep 11, 2008 #1
    How do i find the angles in the triangle with the vertices at [2,-1,0], [5,-4,3], and [1,-3,2]. This problem has been bothering me because when i find the angle between the vectors it only adds to roughly 110 degrees, and that cannot be right.
  2. jcsd
  3. Sep 11, 2008 #2


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    To find the angle between two vectors you can use

    [tex]u\cdot v=|u||v|\cos{\theta}[/tex]
  4. Sep 11, 2008 #3
    I have tried this, but the sum of the three angles only equals 110 not 180.
  5. Sep 11, 2008 #4


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    nicksauce's approach should work here. You should be careful of the directions the vectors point and the angle between them. The angle between the tail of a vector and and the head of another vector is not the same as the one given by the dot product.
  6. Sep 12, 2008 #5


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    Another way which doesn't involve vectors would be to find the lengths of the triangle by calculating distance between points, then apply cosine rule. A purely geometrical approach.
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