Use Descartes' Rule of Signs to determine the possible numbers of positive and negative real zeros.
f(x) = - 9x^4 + 5x^3 - 9x^2 + 6x+7
If there is more than lone possibility, separate them with commas.
(a) Possible numbers) of positive real zeros:?
(b) Possible number(s) of negative real zeros:?