Answer:
(x + y + 1)(x + y - 1)
Step-by-step explanation:
[tex] {x}^{2} + {y}^{2} + 2xy - 1 \\ \\ = {(x + y)}^{2} - {(1)}^{2} \\ \\ = (x + y + 1)(x + y - 1)[/tex]
