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Homework Help: Another vector

  1. Sep 16, 2007 #1
    Given d1 + 8d2 = 5d3, d1 - d2 = 9d3, and d3 = 2 i + 4 j, what are the following vectors?

    (a) d1 =
    (b) d2 =

    I keep trying to do substituting equations, but I am getting them wrong, and help?
     
  2. jcsd
  3. Sep 16, 2007 #2

    Dick

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    You'll need to show an example of how you are getting them wrong before anyone can help. It's actually a pretty easy problem.
     
  4. Sep 16, 2007 #3
    easy, fooled me then
    D3=2i+4j
    d1=5d3-8d2
    d2=-9d3+d1

    so i am trying to combine these to give me the value of either only d1 or only d2, and no matter how I mess with them, I can't seem to be able to do it.

    d1=10i+20j-18j-36j-d1 so I cant do this, plus its wrong

    idk did I mess up the subbing eq's?
     
  5. Sep 16, 2007 #4

    Dick

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    Try subtracting the first two equations from each other. Doesn't that get rid of d1?
     
  6. Sep 16, 2007 #5
    could you be a a little more specific and in dx-dy and do you mean set equal or subtract?
     
  7. Sep 16, 2007 #6
    You could do either a substitution or a subtraction. You will either see that d1 = blah, or eqn1 - eqn2 = something*d2 = blap - bleh.
     
    Last edited: Sep 16, 2007
  8. Sep 16, 2007 #7

    Dick

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    I mean (d1+8d2)-(d1-d2)=5d3-9d3. What's that?
     
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