# Thread: Find this polynomial using this graph.

1. ## Find this polynomial using this graph.

G'day,
I have created a graph on excel and have tried to extract the polynomial (I think that is what it is) but excel tells me the wrong polynomial.

Please open the doc file and extract the polynomial from the graph's data. The first graph is the graph I need the polynomial for. The second is the polynomial that excel gives me which is incorrect.

The first lot of data is for the graph that I want the polynomial for. The second lot of data is the data from the polynomial that excel gave which is incorrect.

This is for private purposes and not for schooling of any type.

I would greatly appreciate your help.

2. ## Re: Find this polynomial using this graph.

Extract the polynomial? I think you mean approximate your data using a polynomial. You cannot model your data perfectly using a polynomial, because your data is rough and not smooth while a polynomial is a perfect mathematical curve, so you are just telling excel to try and find a polynomial that fits your data as closely as possible. Here the coefficient of determination for the polynomial $0.0088 x^2 - 0.11x + 16.565$ is $0.9707$ which means it is a very good (almost perfect, in fact) approximation of your data.

At least that's what I understand from your question. Feel free to clarify if I missed your point.

3. ## Re: Find this polynomial using this graph.

Originally Posted by Bacterius
Extract the polynomial? I think you mean approximate your data using a polynomial. You cannot model your data perfectly using a polynomial, because your data is rough and not smooth while a polynomial is a perfect mathematical curve, so you are just telling excel to try and find a polynomial that fits your data as closely as possible. Here the coefficient of determination for the polynomial $0.0088 x^2 - 0.11x + 16.565$ is $0.9707$ which means it is a very good (almost perfect, in fact) approximation of your data.

At least that's what I understand from your question. Feel free to clarify if I missed your point.
The polynomial that excel gives seems to be the general shape of the data. However, as in graph 2 (the graph of the polynomial excel gives me) the curve goes up around x=13 to x=30 mark, whereas the curve in graph 1 goes up around the x=173 to x=871 mark. So the polynomial $0.0088 x^2 - 0.11x + 16.565$ is the general shape of the data in question, but it doesn't actually fit the data.