now, recall Descartes Rule of Signs. Check the picture below.
the +x part, gives us the positive Real zeros, and it depends on how many times the sign changes from term to term, notice in the picture, it changed 3 times, so the positive real ones are 3, or 3-2, namely 1, so 3 or 1.
the negative real ones, come from using -x as the argument on f(x), and as you can see in the picture, there was only 1 sign change, meaning the negative real zeros are only 1.
since, based on the fundamental theorem of algebra the polynomial has 4 roots at most then,
3 positive real ones, and 1 negative real one, no complex ones
or
1 positive real one, and 1 negative real one, and 2 complex ones
bear in mind that complex always come in pairs, never alone.
