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Cant get to grips with re arranging formulae

  1. Nov 2, 2008 #1
    1. The problem statement, all variables and given/known data

    basically i can't get to grips with rearranging formulae

    the question is

    make U the subject

    fv = uv
    u+v

    (uv is divded by u+v)




    2. The attempt at a solution

    i try at making them into brackets etc but i can't get to it


    can someone show me step by step how to do it


    thanks, much appreciated
     
  2. jcsd
  3. Nov 2, 2008 #2

    Hootenanny

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    Welcome to Physics Forums.

    We won't show you how to do the question, but we will help you do it yourself.

    When trying to make something the subject of a formula the best thing to do is to get it out of the fraction. How could you get (u+v) out of the fraction?
     
  4. Nov 2, 2008 #3
    erm, put it on the other side of the formula?
     
  5. Nov 2, 2008 #4

    Hootenanny

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    Sounds good. So what does that give you?
     
  6. Nov 2, 2008 #5
    fv(u+v)=uv ?
     
  7. Nov 2, 2008 #6

    Hootenanny

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    Looks good. What do you think the next step would be?
     
  8. Nov 2, 2008 #7
    erm multiply out the brackets?
     
  9. Nov 2, 2008 #8

    Hootenanny

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    Sounds good.
     
  10. Nov 2, 2008 #9
    so would it be


    fu+fv+vu+v(squared)=uv
     
  11. Nov 2, 2008 #10

    Hootenanny

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    Not quite, note that to expand the bracket you would just multiply everything in the bracket by fv. Do you follow?
     
  12. Nov 2, 2008 #11
    i dont quite understand that bit
     
  13. Nov 2, 2008 #12

    Hootenanny

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    Okay what is 2(3+4)?
     
  14. Nov 2, 2008 #13
    answer is 14
     
  15. Nov 2, 2008 #14

    Hootenanny

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    Correct, which is the same as 2x3 + 2x4. Does it make sense now?
     
  16. Nov 2, 2008 #15
    er no hah

    i dont see how my answer is wrong
     
  17. Nov 2, 2008 #16
    would it be FVU+FV(squared) = UV
     
  18. Nov 2, 2008 #17

    Hootenanny

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    Much better :approve:.

    What do you suppose the next step is?
     
  19. Nov 2, 2008 #18
    i actually have no idea
     
  20. Nov 2, 2008 #19

    Hootenanny

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    Try moving all the terms with u in onto the same side.
     
  21. Nov 2, 2008 #20
    so then it would be

    fv(squared) = uv-fvu?
     
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