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Homework Help: Vector Proofs

  1. Jan 21, 2008 #1
    1. The problem statement, all variables and given/known data
    I don't know if I'm posting in the right area, but here is the question:
    From the inequality: la dot bl= lal lbl lcos(theta)l is less than or equal to lal lbl

    Deduce the triangle inequality:
    la + bl is less than or equal to lal +lbl

    2. Relevant equations

    3. The attempt at a solution

    I am not even sure where to begin :(
    I'm wondering if I could use numbers to prove it, but that doesn't seem right.
  2. jcsd
  3. Jan 21, 2008 #2
    Sorry, misread. Think about (|a| + |b|)^2. You also have a property available to you that says |a|^2 = a dot a.
    Last edited: Jan 21, 2008
  4. Jan 21, 2008 #3
    |a+b|^2 =(a+b)dot(a+b) is a very nice identity application.
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