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What does this vector equal to?

  1. Apr 27, 2010 #1
    1. The problem statement, all variables and given/known data
    Prove that |[tex]\vec{A}[/tex]|2+|[tex]\vec{B}[/tex]|2 equals to [tex]\frac{1}{2}[/tex](|[tex]\vec{A}[/tex]+[tex]\vec {B}[/tex]|2+|[tex]\vec{A}[/tex]-[tex]\vec{B}[/tex]|2)

    2. Relevant equations
    Perhaps the triangle inequality? I am not sure.

    3. The attempt at a solution
    I have no idea how to approach this question. Please help me with clear explanations. Thank you.
  2. jcsd
  3. Apr 27, 2010 #2


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    Science Advisor
    Homework Helper

    Hi Cuisine123! :smile:

    Use the definition of modulus: |A + B|2 = (A + B).(A + B) etc :wink:
  4. Apr 27, 2010 #3

    D H

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    Staff Emeritus
    Science Advisor

    Perhaps not the triangle inequality. That is an inequality. You are looking for an equality.

    Have you tried expanding the right hand side?
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