1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Modeling with power functions

  1. Dec 27, 2006 #1
    Modeling with power functions.

    I have turned to every book i own on math from algebra to math encyclopedia to calculus ab book. I seriously don't know how to come up with a power function for a set of data. I don't even know any techniques. There are no zeros or intercepts to this set of data.if anyone could please help me come with this function. i dont even know where to start or how.
    x y
    32 6
    48 14
    64 24
    80 38
    96 55
    112 75
    OK may be im stupid but i'm in calc and yes i dont know how to come with a function. so please help.
  2. jcsd
  3. Dec 28, 2006 #2

    Gib Z

    User Avatar
    Homework Helper

    [tex]y=(1.9\cdot 10^{-5})x^3 + 0.004x^2 + 0.052x - 0.0622[/tex]
    [tex]y = (1.1\cdot 10^{-7})x^4 + (2.2\cdot10^-5)x^3 + 0.0019x^2 + 0.208x - 3.28[/tex]
    They both fit pretty well, but the 2nd one fits better i think.

    You know how to find the derivative at a point yes? Look up Taylor series on wikipedia and on this forum, it'll help alot. FYI i didnt get that approximation through that Method, I used my computer. More data points will get a more accurate curve, post more data if you want.
    Last edited: Dec 28, 2006
  4. Dec 28, 2006 #3


    User Avatar
    Science Advisor
    Homework Helper

    The usual way to fit a power function y = Ax^b is to take logs and fit the straight line (log y) = (log A) + b (log x)

    A search for "Least squares method" should find more details.
  5. Dec 28, 2006 #4
    i cant use technology for this i have to derive it myself.
  6. Dec 28, 2006 #5
    im not aware of that method i'll try it. does anyone else have any ideas?
  7. Dec 28, 2006 #6


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Please don't post the same question multiple times.
  8. Dec 28, 2006 #7
    i didnt post twice. i posted in math forum first not realizing there's a homework forum. i'm new here. i dont quiete get the method you told me about. anymore ideas?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Modeling with power functions
  1. Power function (Replies: 2)