Resposta:
[tex]c) \: ( x - \frac{y}{2} ) \times (x + \frac{y}{2} ) \\ \\ {x}^{2} - {( \frac{y}{2} )}^{2} \\ \\ {x}^{2} - \frac{ {y}^{2} }{4} [/tex]
[tex]d) \: (2x + 5) \times (2x - 5) \\ 4 {x}^{2} - 10x + 10x - 25 \\ 4 {x}^{2} - 25[/tex]
[tex]e) \: (x - 3) \times (x + 3) \\ {x}^{2} + 3x - 3x - 9 \\ {x}^{2} - 9[/tex]
