A graph shows zeros near -1.449 and +3.449. These suggest that one factor is the quadratic (x -1)² -6. That makes the other quadratic factor be (x -0.5)² +0.75. So, the complete factorization in integers is
... f(x) = (x² -2x -5)(x² -x +1)
The two real roots are near ...
... d. -1.4, 3.4