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Question involving vector & magnitude

  1. Mar 13, 2012 #1
    1. The problem statement, all variables and given/known data
    "If a vector magnitude 10 is combined with a second vector, the two vectors have a sum with a magnitude of 18 and have a difference with a magnitude of 2√10. Rounded to the nearest hundredth of a degree, what is the measure of the smallest angle between the two vectors?


    2. Relevant equations

    cosθ = (u dotproduct v) / (|u||v|)

    3. The attempt at a solution

    : |u| = 10
    : |u+v| = 18
    : |u-v| = 2√10


    Can you tell me if I'm doing this the right way? If I am, how should I solve this?
     
  2. jcsd
  3. Mar 14, 2012 #2

    vela

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    Looks fine so far. Now square the last two equations and write the lefthand sides in terms of the dot product.
     
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