Find coefficents given equation and three points

1. Sep 26, 2011

Hkskyy

Hello,

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

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

or

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. Sep 26, 2011

TheoMcCloskey

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.

3. Sep 26, 2011

Hkskyy

Thanks much Theo. I was making it more complicated than it should be.