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Homework Help: I need help! Can someone help me with this problem?

  1. Apr 19, 2007 #1
    What is the length of the resultant vector of combining 2A - 3B where vector A= 4i + 3j and vector B= 9i + 8j?
     
  2. jcsd
  3. Apr 19, 2007 #2

    J77

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    First thing is to multiply the vectors by the given amounts... post your result.
     
  4. Apr 19, 2007 #3
    is it -19i + 30j?
     
  5. Apr 19, 2007 #4

    J77

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    No, what's 2A and 3B?
     
  6. Apr 19, 2007 #5
    2A = 8i + 6j
    3B = 27i + 24j

    is that correct???
     
  7. Apr 19, 2007 #6

    J77

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    Yep -- now do the subtraction.
     
  8. Apr 19, 2007 #7
    so (8i + 6j)-(27i + 24j)?
     
  9. Apr 19, 2007 #8

    J77

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    Yeah. What's it equal?
     
  10. Apr 19, 2007 #9
    is it -19i - 18j?
     
  11. Apr 19, 2007 #10

    J77

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    Yeah -- and the length (magnitude) is...
     
  12. Apr 19, 2007 #11
    i'm stuck at that!
     
  13. Apr 19, 2007 #12

    cristo

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    Staff Emeritus
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    The magnitude of a vector [itex]x\vec{i}+y\vec{j}=\sqrt{x^2+y^2}[/itex]. So, what does give you in your case?
     
    Last edited: Apr 19, 2007
  14. Apr 19, 2007 #13
    so is it 26.172?
     
  15. Apr 19, 2007 #14

    J77

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    Yep -- to 3 decimal places.
     
  16. Apr 19, 2007 #15
    Thank you so much!!
     
  17. Apr 19, 2007 #16
    Hello princiebebe57,

    you may find this website here interesting. It contains some questions and answers on vectors.
    If you want to remember the formula for the length of a vector, it helps thinking of the Pythagorean theorem.
     
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