[tex]1\pm\sqrt{2}i[/tex]
Step-by-step explanation:
We already know that one of the roots is x = -4 so we can factor this out to get
[tex]x^3+2x^2-5x+12=(x+4)(x^2-2x+3)[/tex]
Using the quadratic equation on the 2nd factor, we find the roots are
[tex]x= \dfrac{2\pm\sqrt{(2)^2 - 4(1)(3)}}{2}=1\pm\sqrt{2}i[/tex]
