[tex](a - 4b)(a { }^{2} + 4ab + 16ab {}^{2} = [/tex]

[tex](a - 4b)( {a}^{2} + 4ab + 16a {b}^{2} ) \\ = {a}^{3} + 4 {a}^{2} b + 16 {a}^{2} {b}^{2} - 4 {a}^{2} b - 16a {b}^{2} - 64a {b}^{3} \\ = {a}^{3} + 16 {a}^{2} {b}^{2} - 16a {b}^{2} - 64a {b}^{3} [/tex]