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Math Help - Reverse Second Order Logrithm

  1. #1
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    Question Reverse Second Order Logarithm

    Hi all

    I hopw this is the correct forum for this post, but here goes.

    I have the following equation :-

    y=a+b*log(x) + c*log(x)^2

    This basically describes the power conversion efficiency from AC Watts input (x) to DC Watts output (y) for a power supply.

    I need to reverse the equation so that I can find the AC Watts input (x) from the DC Watts output (y).

    This has got me stumped

    Cheers

    Andy
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  2. #2
    MHF Contributor

    Joined
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    Quote Originally Posted by Duckfather View Post
    Hi all

    I hopw this is the correct forum for this post, but here goes.

    I have the following equation :-

    y=a+b*log(x) + c*log(x)^2

    This basically describes the power conversion efficiency from AC Watts input (x) to DC Watts output (y) for a power supply.

    I need to reverse the equation so that I can find the AC Watts input (x) from the DC Watts output (y).

    This has got me stumped

    Cheers

    Andy
    Let u= log(x). Then your equation is y= a+ bu+ cu^2. Solve that with the quadratic formula and then x= 10^u (I am assuming that your log is the "common log" to base 10).
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