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Rearrange Equation

  1. Mar 14, 2007 #1

    I've spent ageees trying this . . .

    Re-arrange to find A:

    (A + Bh) / (2B + A/h) = X

    * / indicates division

    I would post my attempts although it would take me a while to do s and it probably wouldnt give anyone any insight.

    I'd much appreciate it if someone could re-arrange that to for me to find A please.

  2. jcsd
  3. Mar 14, 2007 #2


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    Homework Helper

    What did you try? At least post an attempt at a final answer so we can maybe get an idea of what you're doing wrong. I could give you the answer, but that doesn't help you learn how to do it for next time. The steps to solving this are cross-multiplying, expanding, grouping like terms, and then isolating A. Which part do you think is causing you the most difficulty?
  4. Mar 14, 2007 #3


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    What did you do after you multiplied both sides by (2B+A/h)?
  5. Mar 14, 2007 #4


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    We're not going to simply give you the answer! What have you tried? If I were solving this, I'd make the 1/h in the denominator go first, then multiply the whole equation by the denominator of the LHS...
  6. Mar 14, 2007 #5


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    Staff: Mentor

    I won't give you the answer (you know we won't), but I'll give you hints for the first few steps.

    Get rid of the fraction on the left by multiplying both the left and right hand sides by the denominator of the fraction.

    Multiply out the RHS (right hand side). That is, distribute X into the two terms in the parenthesis.

    Now you want to gather up terms that have the A in them....

    Do those steps here so we can see how you do. If you get that far, you'll probably see the final steps on your own, but we can help more at that point if you need it.
  7. Mar 14, 2007 #6


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    Holy Smokes! Homework Helper pile on!! :biggrin:
  8. Mar 14, 2007 #7
    Some Help

    The guidelines of the help section specifically state that people are not supposed to just answer questions but rather give help instead. So, here is some help.

    Step1: Combine 2B + A/h into a single fraction.
    Step2: Divide A + Bh by the fraction you just obtained. (remember A + Bh can be written as (A + Bh)/1, and that to divide a fraction by a fraction you can flip the bottom and multiply.
    Step3: This fraction answer is = to X
    Step4: Multiply both sides by the entire quantity of the denominator.
    Step5: Bring everything with an A to one side of the equation and everthing else to the other side.
    Step6: Factor out the A on the one side.
    Step7: Divide both sides by the remaining quantity you just separated the A from, and you have your answer.

    Good Luck.
  9. Mar 15, 2007 #8
    Sorry . . . I meant to say re-arrange for h. I want to isolate h.

  10. Mar 15, 2007 #9


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    Dearly Missed

    So, what have you done so far? :smile:
  11. Mar 15, 2007 #10
    Berkeman's advice still works. Replace A in the third step with h.
  12. Mar 19, 2007 #11
    yeah but the answer comes out as a quadratic
  13. Mar 19, 2007 #12
    son of a gun, so it does.

    I assume you had something like
    A + Bh = 2Bx + AX/h
    and you multiplied everything on both sides to get rid of h in the denominator.

    [tex]Ah + Bh^2 = 2BXh + AX [/tex]
    And, you're solving for h.

    No problem... How would you solve this equation for h:
    4h^2 + 3h - 17 = 0?

    Solve this equation the same way: (3m)h^2 + (5+w)h + (r-t) = 0

    Now, can you put the equation you had with h^2 into the form of a quadratic equation and solve it?

    There's also another method called "complete the square" that would work. In fact, that method is used to derive the quadratic formula, so the quadratic formula is, more or less, a short-cut (sort of). Then again, knowing both methods, sometimes the quadratic formula works out much more quickly, and sometimes, completing the square works out much more quickly. They're both good tools to have in your arsenal of attacking problems.
  14. Mar 19, 2007 #13


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    Staff: Mentor

    So, do you know how to use the quadratic formula to solve a quadratic equation?
  15. Mar 20, 2007 #14
    Thanks ppl!

    Much appreciated. I can do it from here

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