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Math Help - Power Regression

  1. #1
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    Power Regression

    I have a Math Internal Assessment that I'm doing (basically a Math Essay...) and for one of the parts I have to find an equation for the data given. I have tried all the regressions on my calculator and found that Power Regression gives the best equation that fits the graphed data. I have a program on my computer that can do power regression, though I need to know how to do the power regression by hand (I have to "show" how I got that graph).

    any input would be appreciated and sorry if this is the wrong forum because I don't really have any idea where it should go.

    I know that the formula is ax^b, but I do not know what a nor b stands for...
    Last edited by motoxcreature; September 10th 2009 at 08:53 AM.
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  2. #2
    MHF Contributor Calculus26's Avatar
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    I'm not sure how much by hand you want to do

    but you basically are doing a log- log plot

    y= a x^b

    lny = ln(a) + bln(x)

    so graph your points on a ln(y) versus ln(x)


    the slope is b and the intercept is ln(a)
    Last edited by Calculus26; September 10th 2009 at 10:02 AM.
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  3. #3
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    So basically I start off with the equation y=mx+b and from that I use m=b and b=a?
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  4. #4
    MHF Contributor Calculus26's Avatar
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    yes but perhaps I chose a confusing choice of variables

    Let

    y= ax^t

    ln(y) = ln(a) + tln(x)

    m =t c = ln(a)

    and a = e^(c)
    Last edited by Calculus26; September 10th 2009 at 10:02 AM.
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  5. #5
    MHF Contributor Calculus26's Avatar
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    Correction

    See edits to previous posts

    I wrote y = ab^x instead of ax^b

    sorry

    At some point you'll need technology

    I've included an example where I used Mathcad to do a power regression
    Attached Files Attached Files
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  6. #6
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    thanks for all your help. And yes, I know that I do need to use technology at some point to for it, though I need to make sure that they know that I am using some math instead of just using technology for everything.

    And thanks for the mathcad .pdf, I have mathcad and I guess I'll install that now and use it (it's way better than excel, except more confusing...)
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  7. #7
    MHF Contributor Calculus26's Avatar
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    If interseted I've created 2 web sites using Mathcad

    Calculus Animations which is a collection of animations and lecture notes

    and what may be of more immediate use for learning the basics of mathcad

    Creating Animations Using Mathcad
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