Online Algebra Calculator
Many of users do not use powerful Maxima computer algebra system for systematic work, but for ad hoc algebraic calculations – equations, functions, matrixes, etc. only. To do this job, it is not useful to download the whole application from a web site.
Function: nroots (<p>, <low>, <high>) Returns the number of real roots of the real univariate polynomial <p> in the half-open interval (<low>, <high>]. The endpoints of the interval may be minf or inf. infinity and plus infinity.

nroots uses the method of Sturm sequences.
(%i1) p: x^10 - 2*x^4 + 1/2$
(%i2) nroots (p, -6, 9.1);
(%o2) 4(%o1) true (%i2)