Descartes' rule of signs

Descartes' Rule of Signs For a polynomial $P(x)$:
$\bullet$ the number of positive roots = the number of sign changes in $P(x)$, or less than the sign changes by a multiple of 2.
$\bullet$ the number of negative roots = the number of sign changes in $P(-x)$, or less than the sign changes by a multiple of 2.

Note: Before applying the Descartes' Rule of Signs, make sure to arrange the terms of the polynomial in descending order of exponents.