Resposta:
Boa noite!
Explicação:
Vamos lá!
[tex](7- x).(7 + x) =\\\\49+7x-7x-x^2\\\\-x^2+49\\\\\\Resolvendo...\\-x^2+49=0\\\\-x^2=-49\ \centerdot(-1)\\\\x=\sqrt{49} \\\\\boxed{x=7}[/tex]
