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Find coefficents given equation and three points

  1. Sep 26, 2011 #1

    I hope someone can help me with this. I have an equation:

    log10(y) = a * log10(x) + b


    y = 10^(log10(x)a + b)

    I am trying to find a and b given two points. My approach is to use the process of simultaneous equation but I am having problems subtracting the equations.

    Points: (5, 20) (10,2)

    first equation: 20 = 10^(log10(5)a +b)
    second equation: 2 = 10^(log10(5)a +b)

    Subtraction: 18 = 10^(log10(5)a +b) - 10^(log10(5)a +b)

    My question is if this is a good approach and if I am following the laws. I am trying to fit the equation to the two points.

    Thanks all,
    Last edited: Sep 26, 2011
  2. jcsd
  3. Sep 26, 2011 #2
    Hkskyy - use your first form of the expression with the two points. This will set up two linear equations in a and b that you can solve.
  4. Sep 26, 2011 #3
    Thanks much Theo. I was making it more complicated than it should be.
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