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July 21st, 2016, 02:54 AM  #1 
Newbie Joined: Jul 2016 From: England Posts: 2 Thanks: 2  Predicting outcome formula
Hi all, I was hoping someone might be able to help me with a maths related question. I'm wondering if there is a formula for predicting the value of something based on precedence. So for example: If 90 = 280, 100 = 250 and 110 = 230, what does 120 equal? (these numbers are just examples) Thanks! 
July 21st, 2016, 01:32 PM  #2 
Global Moderator Joined: May 2007 Posts: 6,755 Thanks: 695 
The simplest function to fit 3 points is a parabola. Get the 3 coefficients by using the 3 values you have and then compute the value at the fourth point. parabola $\displaystyle y=ax^2+bx+c$. (x,y) pairs are (90,280), (100,250), (110,230). You now have 3 equations in 3 unknowns (a,b,c). 
July 22nd, 2016, 12:21 AM  #3 
Newbie Joined: Jul 2016 From: England Posts: 2 Thanks: 2 
Hi, thanks for getting back to me. I am extremely new to this so there are a few things I don't understand. In the formula you shared, is Y the number I'm looking for? And what is X? 
July 22nd, 2016, 01:32 PM  #4 
Global Moderator Joined: May 2007 Posts: 6,755 Thanks: 695 
(x,y) is a general point on the curve. You know three specific points and you are (assuming a parabola) getting the general formula. Once you have the formula, then let x=120 to get what you are looking for (=y).

July 22nd, 2016, 07:54 PM  #5 
Senior Member Joined: Dec 2015 From: holland Posts: 162 Thanks: 37 Math Focus: tetration 
The answer is 220 it is a second degree polynome.


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