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Homework Help: Angle between two vectors

  1. Feb 2, 2012 #1
    Hello, Ive been trying to solve this problem for hours now, but i keep getting it wrong. Been looking for examples but i dont seem to find one with a good explanation, so any help is appreciated.

    The problem:

    Consider two displacements, one of magnitude 2.6 and another of magnitude 3.9. What angle between the directions of these two displacements give a resultant displacement of magnitude a) 5.7m b)2.6m c)3.2

    If anyone can please help me understand, thank you. Please, dont just post the answer, i want to learn how to solve it.
  2. jcsd
  3. Feb 2, 2012 #2


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    Staff: Mentor

    This is referring to addition of the displacements.

    You have a triangle, and know the lengths of the 3 sides. Find the angle/s.
  4. Feb 2, 2012 #3


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    Science Advisor

    A formula that will help is the cosine law. If a triangle has sides a, b, and c and C is the angle opposite side c, then [itex]c^2= a^2+ b^2- 2ab cos(C)[/itex]
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