Descartes’ rule of sign is used to determine the number of real zeros of a polynomial function. It tells us that the number of positive real zeroes in a polynomial function f(x) is the same or less than by an even numbers as the number of changes in the sign of the coefficients.Click to see full answer. Subsequently, one may also ask, how many negative real zeros does the function?Since we have 4 sign changes with f(x), then there is a possibility of 4 or 4 – 2 = 2 or 4 – 4 = 0 positive real zeros. Note how there are no sign changes between successive terms. This means there are no negative real zeros.Furthermore, what is a real zero? Real Zeros. Recall that a real zero is where a graph crosses or touches the x-axis. Think of some points along the x-axis. Moreover, why does Descartes rule of signs work? Descartes’ rule of sign. Descartes’ rule of sign is used to determine the number of real zeros of a polynomial function. It tells us that the number of positive real zeroes in a polynomial function f(x) is the same or less than by an even numbers as the number of changes in the sign of the coefficients.How many real roots does the equation have? Total Number of Roots On the page Fundamental Theorem of Algebra we explain that a polynomial will have exactly as many roots as its degree (the degree is the highest exponent of the polynomial). So we know one more thing: the degree is 5 so there are 5 roots in total.