Question

(PUC -77) O domínio da relação P = { (x, y) ∈ N × N ; y = x – 5} é:

Answer 1

Olá!

Note que $\mathbf{y \in \mathbb{N}}$. Ou seja,

$\\ \mathsf{y \in \mathbb{N}; y \geq 0} \\\\ \Downarrow \\\\ \mathsf{y \geq 0} \\\\ \mathsf{x - 5 \geq 0} \\\\ \mathsf{x \geq 5}$

 Isto é, 

$\boxed{\mathsf{Dom \, (P) = \left \{ x \in \mathbb{N}; x \geq 5 \right \}}}$