Răspuns:
Explicație pas cu pas:
x*y = xy + x + y + 4
2020*(-1) = ?
x = 2020
y = -1
2020*(-1) = -2020 + 2020 - 1 + 4 = 3
__________
xy + x + y + 4 = xy + x + y + 1 + 3 = x(y + 1) + (y + 1) + 3 = (y + 1)(x + 1) + 3
⇒ x*y = (y + 1)(x + 1) + 3
___________
m*n = mn + m + n + 4 = 2
mn + m + n + 4 - 2 = 0
mn + m + n + 2 = 0
mn + m + n + 1 + 1 = 0
m(n + 1) + (n + 1) + 1 = 0
(n + 1)(m + 1) = -1
n + 1 = 1 si m + 1 = -1
n = 0 si m = -2
sau
n + 1 = -1 si m + 1 = 1
n = -2 si m = 0
perechile sunt (-2, 0); (0, -2)
