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Homework Help: Help with vectors.

  1. Sep 19, 2005 #1
    First I want to say hello to everyone in here. I'm a noob.

    Here is my problem.
    Let u=(1.2.0), v=(0,0,3), and w=(0,1,0) are vectors in R^3.
    Evaluate, if defined, the following expretions (if undefined state so)

    a) (u * v)w
    b) u+w*v
    c) (u * u)/w
    d) (v * v)/(w * w)


    Should I try to calculate them or just tell if expretion is defined or undefined?
    How can I tell if expretions above are defined?
     
  2. jcsd
  3. Sep 19, 2005 #2

    James R

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    Read the instructions in the question!

    Is "*" supposed to represent a dot product, or cross product?
     
  4. Sep 19, 2005 #3
    It is a dot product.
     
  5. Sep 19, 2005 #4

    EnumaElish

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    "Evaluate" means "calculate."

    If you calculate and get a definite answer (a real number or vector) then it is defined.
     
  6. Sep 20, 2005 #5
    Are my answers correct?

    a) 0
    b) undefined ( I don't see how I can add scalar to vector)
    c) undefined
    d) 9
     
  7. Sep 20, 2005 #6

    HallsofIvy

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    a, b, c are correct (you are correct that you can't add a scalar to a vector. In c, division by a vector is not defined). However, in
    d) (v * v)/(w * w)
    The answer is clearly a fraction.
     
  8. Sep 21, 2005 #7

    James R

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    The answer to (d) is correct. It's 9.
     
  9. Sep 22, 2005 #8

    HallsofIvy

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    Hey, 9/1 is a fraction!! (blushing)
     
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