Respuesta :

21x^3+6x^2-28x-8
(21x^3+6x^2)-(28X+8)
3x^2(7x+2)-4(7x+2)
3x^2-4=0 and 7x+2=0
Exvited
[tex]21x^3 + 6x^2 - 28x - 8 \\ \\ 3x^2 (7x + 2) - 4(7x + 2) \\ \\ (7x + 2)(3x^2 - 4) \\ \\ [/tex]

The final result is: (7x + 2)(3x² - 4).