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Dot Product

  1. Jan 13, 2016 #1
    1. The problem statement, all variables and given/known data
    9uc4zs.jpg

    2. Relevant equations
    p.q+p.r

    3. The attempt at a solution
    I've expanded p.(q+r) to give p.q+p.r. The magnitude of p is 3, and since ABE is an equilateral triangle, the magnitude of q is also 3, right? So then p.q=9, but the answer scheme states that p.q=4.5.
    I'm still pretty new to mathematics, so I'm probably missing something really obvious, but it's better to make the mistakes now than in my exam!
     
  2. jcsd
  3. Jan 13, 2016 #2

    Samy_A

    User Avatar
    Science Advisor
    Homework Helper

    p.q is certainly not equal to 9.

    Maybe you could start by stating the geometric definition of the dot product in Euclidean space, or ##\mathbb R^3## in this case.
    Then you will be able to deduce from that the values of p.q and p.r
     
  4. Jan 13, 2016 #3
    Ah, I've got it now. Thanks for your help!
     
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