Use Descartes' rule of signs to determine the possible number of:

a) positive real roots of $\displaystyle 4x^3 + 2x^2 + 7x + 9 = 0$

b) negative real roots of $\displaystyle 4x^3 + 2x^2 + 7x + 9 = 0$

My answer to a) (zero positive real roots), was correct.

Zero positive real roots because there are zero sign changes..

and I had thought there would be zero negative roots as well. But it came back wrong.

Can someone explain to me why? Thanks.