How to find the f(x) (least square method)

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The discussion revolves around finding the function f(x) using the least squares method to complete a data chart. The user provides a set of values for x, y, x^2, and xy but is unsure how to derive f(x). Respondents clarify that the provided values do not directly indicate a specific function and suggest searching online for examples of the least squares method. The user emphasizes their intention to complete the work independently, seeking only a memory jog. Overall, the conversation highlights the need for additional context or information to accurately determine f(x).
mjmara
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Hi my first post , I hope I chose the right forum?

I'm here looking for a memory jog not for someone to do my work, I'm trying to remember how to find the f(x) to complete this chart , there is many more data points but I'm just providing you with the top line , I shall do the rest myself, can someone help me please?
It's been many years since I attempted this problem :(


x y x^2 xy f(x) f(x)-y (f(x)-y)^2
________________________________________________
-8 6.8 64 -54.4 ?
 
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sorry

the format is all messed up

here

x___y___x^2___x.y____f(x)
-8__6.8__64____-54.4__?sorry for the format but this is the best I can do

x= -8
y= 6.8
x^2 = 64
x.y = -54.4
f(x) = ?
 
It still is not at all clear what you are asking. Yes, if x= -8 and y= 6.8, then x^2= 64 and xy= -54.4 but that has nothing to do with some function, "f". Do you have any other information?
 
mjmara said:
I'm here looking for a memory jog not for someone to do my work, I'm trying to remember how to find the f(x) to complete this chart
A google search on method of least squares will find some good examples for you to follow, if I have you right. Here is one that may help.
 
I tried to combine those 2 formulas but it didn't work. I tried using another case where there are 2 red balls and 2 blue balls only so when combining the formula I got ##\frac{(4-1)!}{2!2!}=\frac{3}{2}## which does not make sense. Is there any formula to calculate cyclic permutation of identical objects or I have to do it by listing all the possibilities? Thanks
Since ##px^9+q## is the factor, then ##x^9=\frac{-q}{p}## will be one of the roots. Let ##f(x)=27x^{18}+bx^9+70##, then: $$27\left(\frac{-q}{p}\right)^2+b\left(\frac{-q}{p}\right)+70=0$$ $$b=27 \frac{q}{p}+70 \frac{p}{q}$$ $$b=\frac{27q^2+70p^2}{pq}$$ From this expression, it looks like there is no greatest value of ##b## because increasing the value of ##p## and ##q## will also increase the value of ##b##. How to find the greatest value of ##b##? Thanks
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