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I need help with this problem!

  1. Sep 13, 2003 #1
    1/a+h+9 - 1/a+9 divide by h

    This is a function and I suppose to calculate the value. But im stuck. Thanks for your help.
     
  2. jcsd
  3. Sep 13, 2003 #2

    enigma

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    Hi Learning, welcome to the forums!

    Let me ask for clarification. You don't have any parenthesis, so the equation is a little ambiguous when looking at the screen.

    Is this the equation:

    1/(a+h+9) - (1/(a+9))/h

    or is it something different?
     
  4. Sep 13, 2003 #3
    Thats exactly right, sorry I forgot the those. Its different on the computer than writing it. Thanks
     
  5. Sep 13, 2003 #4

    enigma

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    Re: Re: I need help with this problem!

    Ok,

    Forum rules: you really should try the problem yourself first, so we can help where you got stuck. I can give you some pointers to get you started, though.

    The trick is to get the h by itself on one side.

    1/(a+h+9) - (1/(a+9))/h = 0

    In this case, you'd first add (1/(a+9))/h to both sides, giving

    1/(a+h+9) = (1/(a+9))/h

    Then, multiply both sides by h, giving

    h/(a+h+9) = 1/(a+9)

    Give it a shot, and let us know how you do. Remeber, multiplying by X/X is the same as multiplying by 1.
     
  6. Sep 14, 2003 #5
    Thanks for your help engima. Funny thing is thats where im stuck. I keep doing the problem that way, but I don't know where to go from there.
     
  7. Sep 14, 2003 #6

    enigma

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    Multiply both sides by the denominators, then add and subtract the h terms to one side, and all the others to the other side. Collect the coefficients on the h, and divide both sides by them.

    Give it a shot, post your work!
     
  8. Sep 14, 2003 #7
    I'm lost. Please work with me here.
     
  9. Sep 16, 2003 #8

    HallsofIvy

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    First, you will need to learn to be more precise: I noticed that when there was a question as to exactly what you meant, you apologized for not putting in parentheses to make it clear, but DIDN'T tell us what the correct formula was.

    I assume that you mean, not 1/(a+h+9) - (1/(a+9))/h = 0, as enigma said (because there was no equation, initially) but rather,
    (1/(a+h+9)- 1/(a+9))/h simply because that's a fairly standard "derivative" problem.

    The first thing you should do is add the fractions: since they have different denominators, you need to get the same denominator by multiplying the numerator and denominator of the first fraction by (a+9): (a+9)/((a+h+9)(a+9)) and the numerator and denominator of the second fraction by (a+ h+ 9): (a+ h+9)/((a+h+9)(a+9))
    (I did not multiply out the denominator because there is no need to.)

    Now we know
    1/(a+h+9)- 1/(a+9)= (a+9)/((a+h+9)(a+9))-(a+ h+9)/((a+h+9)(a+9))
    = (a+9-(a+h+9))/((a+h+9)(a+9))
    = -h/((a+h+9)(a+9))
     
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