Question

descartes sign theory? tell me how it works please.

Answer 1

good explanation: http://www.purplemath.com/modules/drofsign.htm

Answer 2

basically, you see how many sign changes there are are in f(x) and that's the max number of positive roots. could also be that minus 2, 4, 6, 8... number of positive roots. Then you similarly look at f(-x) for the number of negative roots.