a)
[tex]2x \times ( - x) \times 2(6x + 16)[/tex]
[tex] - 4 {x}^{2} \times (6x + 16)[/tex]
[tex] - {24}^{3} [/tex]
b)
[tex]4 {x}^{3} + {x}^{2} - 5x = 0[/tex]
[tex]x \times (4 {x}^{2} + 5x - 4x - 5) = 0[/tex]
[tex]x = 0[/tex]
[tex]4x + 5 = 0[/tex]
[tex]x - 1 = 0[/tex]
[tex]x = - \frac{5}{4} [/tex]
