The Budan-Fourier Theorem
Given a polynomial of degree , the sequence , , ..., is called the Budan–Fourier sequence of .[more]
Let be the number of real roots of over an open interval (i.e. excluding and ). Then , where is the difference between the number of sign changes of the Budan–Fourier sequence evaluated at and at , and is a non-negative even integer. Thus the Budan–Fourier theorem states that the number of roots in the interval is equal to or is smaller by an even number.[less]
 Wikipedia. "Budan's Theorem." (Mar 20, 2017) en.wikipedia.org/wiki/Budan's_theorem.