Question

Tìm x,y thuộc Z :

a)xy=x+y

b)xy=x-y

(làm rõ ra hộ mik nhé)

Answer 1

chtt

Answer 2

a) => xy - x - y = 0

=> x(y - 1) - y + 1 = 1

=> x(y - 1) - (y - 1) = 1

=> (x - 1)(y - 1) = 1

=> x - 1 = y - 1 = 1 => x = y = 2

hoặc x - 1 = y - 1 = -1 => x = y = 0

Vậy (x;y) \(\in\){(2;2);(0;0)}

 

Answer 3

b) => xy - x + y = 0

=> x(y - 1) + y - 1 = -1

=> x(y - 1) + (y - 1) = -1

=> (x + 1)(y - 1) = -1

=> x + 1 \(\in\)Ư(-1) = {-1;1}

Ta có bảng sau:

x + 1	-1	1
x	-2	0
y + 1	1	-1
y	0	-2

Vậy (x;y) \(\in\){(-2;0);(0;-2)}