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Math Help - I'm working on a project and need some help with a logarithmic function...

  1. #1
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    Dec 2009
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    I'm working on a project and need some help with a logarithmic function...

    Hi all,
    Firstly first post wasn't sure where to put this apologies if it is wrong, and if this is a totally daft post.

    I'm working on a little project for myself and I am having issues with the following:

    I have three variables A B C.

    A is a lower limit,
    B is an upper limit
    C is a ratio of the two.

    Now I have got this far:

    D=10^((C-A)/((B-A)/2))

    This gives a % output where if C=A D=1, if B=C D=~100

    What I am looking to do is have an output that is a ratio of A to B:

    For example:
    If A=C Ratio=0
    If A=B Ratio=

    Hopefully that will make some sense?

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  2. #2
    Member
    Joined
    Nov 2009
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    202

    easy but lengthy

    if u want the ratio between A and B it is:
    B/A=1-2ln10(B-A)/lnD(B-A)-2Cln10

    this was easy . u simply solve the given equation by taking log on both sides.
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  3. #3
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    Dec 2009
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    Sorry perhaps I should have been clearer, although what you said may still apply.

    Ill try with another example.

    As I said A and B are are the upper and lower limits, they can change but C which is physically measured will always land between them.

    I need to find D which is the ratio of A to B. D will always land within 10:1 to 100:1 of A:B.
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