Question

Help:

Answer 1

find the number of sign changes in f(x). The sign changes 3 times: from x4 to x3, from x3 to x2 and from x2 to x. So max number of +ve real roots is 3. Similarly max number of -ve real roots can be obtained by number of sign changes in f(-x), which is 2.

Answer 2

But how do I find positive or negative roots? .__.

Answer 3

you can't. descarte's rule only gives you can upper limit to the number of positive and negative real roots.