Please explain

Question

One factor of x3 + 5x2 + 2x - 8 is (x + 4). Find the remaining factors.

Answer 1

perform either synthetic division or long algebraic division of
(x^3 + 5x^2 + 2x - 8) by (x+4) to get

(x^3 + 5x^2 + 2x - 8) = (x+4)(x^2 + x - 2)

I will leave it up to your to further factor the quadratic, it comes apart very easily.