Ссистемой! x^2-y^2-xy=2 x+y=-2 2xy=?

{ (x - y)(x + y) - xy = 2
{ x+y = -2; y = -2 - x = -(2 + x)
Подставляем
-2(x - y) - xy = 2
-2x + 2y - xy - 2 = 0
-2x - 2(2 + x) + x(2 + x) - 2 = 0
-2x - 4 - 2x + 2x + x^2 - 2 = 0
x^2 - 2x - 6 = 0
D = 2^2 + 4*6 = 4 + 24 = 28 = (2√7)^2
x1 = (2 - 2√7)/2 = 1 - √7; y1 = -2 - x = -3 + √7
2xy = 2(1 - √7)(-3 + √7) = 2(-3 + 4√7 - 7) = -20 + 8√7
x2 = (2 + 2√7)/2 = 1 + √7; y2 = -2 - x = -3 - √7
2xy = 2(1 + √7)(-3 - √7) = 2(-3 - 4√7 - 7) = -20 - 8√7