Please help me understand this!!! :(

According to Descartes' rule of signs, how many possible positive real roots could the following polynomial function have? f(x)=3x^4-5x^3+5x^2+5x-2
A. Four
B. Three
C. Two or zero
D. Three or one

Please help :(

Question

Please help me understand this!!! :(

According to Descartes' rule of signs, how many possible positive real roots could the following polynomial function have? f(x)=3x^4-5x^3+5x^2+5x-2 
A. Four 
B. Three 
C. Two or zero 
D. Three or one

Please help :(

anonymous · Answer

there is a very clear explanation with a good example worked out step by step here http://www.purplemath.com/modules/drofsign.htm

anonymous · Answer

Thanks so much!! :D

anonymous · Answer

in your case the coefficients are 3,-5,5,5,-2 
so there are 3 "changes in sign" for $f(x)$ meaning there are either 3 or 1 positive zero
then you have to compute the coefficients of $f(-x)$ but in order even to understand what i mean by "changes in sign" the puplemath link explains better than i can

anonymous · Answer

Okay! Thanks a ton!! :D