[tex]4) \: {x}^{2} + 11x + 28 = 0 \\ \Leftrightarrow {x}^{2} + 7x + 4x + 28 = 0 \\ \Leftrightarrow x(x + 7) + 4(x + 7) = 0 \\ \Leftrightarrow (x + 4)(x + 7) = 0 \\\Leftrightarrow x = - 4 \: \vee \: x = - 7 \\ \\ 5) \: (3a + 8)(3 {a}^{2} - a - 7) \\ = 9 {a}^{3} - 3 {a}^{2} - 21a + 24 {a}^{2} - 8a - 56 \\ = 9 {a}^{3} + 21 {a}^{2} - 29a - 56[/tex]
