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Inverse f(x)

  1. Jul 11, 2007 #1
    1. The problem statement, all variables and given/known data

    Find inverse of f(x) when f(x) = (2x-5)/(7x+4)

    2. Relevant equations

    none

    3. The attempt at a solution

    x=(2y-5)/(7y+4) and then i get stuck trying to rearrange back to y=...
     
  2. jcsd
  3. Jul 11, 2007 #2

    Dick

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    Where do you get stuck?? Multiply both sides by 7y+4, move all of the terms with a y in them to one side and solve for y. It's not that hard.
     
  4. Jul 11, 2007 #3
    ok that gives x(7y+4) -2y= -5, 7xy+4x-2y=-5, so how do i get it back to y= then genius?
     
  5. Jul 11, 2007 #4

    danago

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    Keep all your terms with 'y' in them on one side, and all the other terms on the other, and then take out a factor of 'y', and it should be clear from there.
     
  6. Jul 11, 2007 #5

    Dick

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    So 4x+5=2y-7xy=y(2-7x). Can you solve for y now, genius?
     
  7. Jul 11, 2007 #6
    haha yep ty
     
  8. Jul 11, 2007 #7

    Dick

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    BTW sorry about the 'it's not that hard' crack. If you don't see it, you don't see it.
     
  9. Jul 11, 2007 #8
    yeah sry bout the genius thing, thanks for the help anyone, much appreciated
     
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