Resposta:

[tex]a) \: 4 {x}^{2} z - 8xz \\ 4xz \times (x - 2)[/tex]

[tex]b) \: {x}^{2} - 81 \\ {x}^{2} - 9 {}^{2} \\ (x - 9) \times (x + 9)[/tex]

[tex]c) \: {x}^{2} - 10x + 25 \\ {x}^{2} - 2 \times x \times 5 + 25 \\ {x}^{2} - 2 \times x \times 5 + {5}^{2} \\ {(x - 5)}^{2} [/tex]