Use the rational zero theorem, Descartes rules of signs, and the theorem of bounds as aids in finding all real and imaginary roots to the equation.
Descartes rules of signs:
States, that the number of transitions from positive to negative (or vise versa) in a polynomial will be the number of roots a polynomial contains.
Here is the signs of the function:
I count 3 there.
But we could also find that using The fundamental theorem of algebra.