[math]f_2-f_1=a_1X+b_1X^2+cX^3[/math][br][math]a_2-a_1=2b_1X+3cX^2[/math][br][math]b_2-b_1=3cX[/math][br][br]About polynomial-states, polynomial-variables, polynomial-functions and polynomial-constants see in [url=https://algebra21blog.wordpress.com/principles/]https://algebra21blog.wordpress.com/principles/[/url].