Use descartes rule of sign to determine the possible number of positive real zeros and possible number of negative 6x^5-6x^4+7x^3-8

Answer 1

f(x) has 3 changes, so 3 or 1 + roots
f(-x) has no sign changes, so no - roots

check:

http://www.wolframalpha.com/input/?i=6x^5-6x^4%2B7x^3-8