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Homework Help: Hey simple vector problem

  1. Aug 14, 2008 #1
    I went through some old vector problems and did over 100 but I couldn't get my hands on this one, thanks for taking your time to help me out.

    Problem: If vectors A and B are added, the resultant has magnitude A. If the two are subtracted, the resultant has a magnitude 2A. If A = 4 what is B and what is the angle between the two vectors.

    Solve using triangles and the law of sinces/cosines, and also solve using the component approach.

    Thanks much.
  2. jcsd
  3. Aug 14, 2008 #2


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    If V is a vector with magnitude |V|, then V.V=|V|^2. So your first condition is (A+B).(A+B)=|A|^2. What's the second one? Expand out the dot products using the distributive property and solve for B.B and A.B. Then remember A.B=|A||B|cos(theta).
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