2x^4 + x^3 − 8x^2 − 4x
= x ∙ (2x^3 + x^2 − 8x − 4)
= x ∙ (x^2 ∙ (2x + 1) − 4 ∙ (2x + 1))
= x ∙ (x^2 − 4) ∙ (2x + 1)
= x ∙ (x − 2) ∙ (x + 2) ∙ (2x + 1)
Thus the roots are:
x ∙ (x − 2) ∙ (x + 2) ∙ (2x + 1) = 0
⇒ [x = 0] or [x − 2 = 0] or [x + 2 = 0] or [2x + 1 = 0]
⇒ [x = 0] or [x = 2] or [x = −2] or [x = − 1/2]
