Examine the number of sign changes for f(x) and f(-x)


There are two sign changes for the coefficient of f(x), so the function has 2 or 0 positive real zeros.

There is 1 sign change for the coefficients of f(-x). So f(x) has one negative real zero.
Thus, f(x) has 2 or 0 positive real zeros, 1 negative real zero, 2 or 4 imaginary zeros