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Dot prodcuts

  1. Sep 15, 2007 #1
    ii think i did this correct ( i hate projections)

    1. The problem statement, all variables and given/known data

    find the scalar and vector projections of b onto a

    2. Relevant equations

    a= (-1, -2 2) b=( 3,3,4)

    scalr (a dot b)\|a|
    vector (a dot b)\|a| * a/|a|

    3. The attempt at a solution


    (a dot b)\|a| =(1 =6 +8)/3 =1/3=scalar
    1/3* (a/|a|)= 1/3 *(1/3)*a =-1/9, -2/9, 2/9
     
  2. jcsd
  3. Sep 16, 2007 #2
    i made a typo!

    i meant to put (-3 -6 +8)/3 =1/3
     
  4. Sep 16, 2007 #3

    dynamicsolo

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    Homework Helper

    (He returns after catching his miscopying of a value...) Check your arithmetic here: there is an error in your dot product calculation. Your method looks all right, so the rest should fall into line from there.
     
  5. Sep 16, 2007 #4
    a dot b

    a = (-1, -2 ,2) b=(3,3,4)

    -1(3) +(-2)(3) +2(8)= -3 +-6 +8..ooooooh -1 hahaa

    is that the erorr you meant
     
  6. Sep 16, 2007 #5

    dynamicsolo

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    I believe that should do it. Everything else looked right -- basically, your vector projection components will just flip sign. Does that get you the right result?
     
  7. Sep 16, 2007 #6
    i think so thanks
     
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