Descartes rule of sign can be used to isolate the intervals containing the real roots of a real polynomial. The rule bounds the number of roots from above, that is, it is exact only for intervals having zero or one root. In methods like VCA, VAS and similar, it is used to count the number of sign changes to determine the number of roots.

My question is, what to do if the rule reports, say, two sign changes for interval which does not contain any roots?

My question is, what to do if the rule reports, say, two sign changes for interval which does not contain any roots?