You quoted 2 degree polynomial in the example. The polynomial function can also be developed from data set. Look at the following document for further explanation. Hopefully it may help. Thank you.

Hola Ramón. Si tienes un conjunto de resultados de la función evaluada puedes utilizar alguna técnica de interpolación para obtener el polinomio de la función. En el siguiente link hay documentación sobre técnicas de interpolación. Saludos

http://nm.mathforcollege.com/topics/textbook_index.html

To obtain a function of your data. Read about the regrission method poly or linear they are helfull to you

You need to change your data according the number of variable and each variable give a unique power for example 3x + 5y + z become 3 + 5x + x2. the x replace with x0 , y to x and z to x2 .