What is the number of possible positive zeros and number of possible negative zeros of this polynomial function: \(f(x)=x^4+2x^3−11x^2−5x−6\)
The coefficient signs run + + - - -, just one change, so Descartes' rule of signs says that there is precisely one positive root.
Replace x by - x to get
\(\displaystyle f (-x)=x^{4}-2x^{3}-11x^{2}+5x-6,\)
and you see three sign changes, indicating three or one negative roots.
