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July 21st, 2016, 02:54 AM   #1
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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!
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July 21st, 2016, 01:32 PM   #2
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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).
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July 22nd, 2016, 12:21 AM   #3
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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?
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July 22nd, 2016, 01:32 PM   #4
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(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).
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July 22nd, 2016, 07:54 PM   #5
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Math Focus: tetration
The answer is 220 it is a second degree polynome.
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