Respuesta :

If  we substitute z = 2 - x - y  in the last 2 equations  it simplifies to 2 equations in x and y:=

x^2 + y^2 + xy - 2x - 2y =  5 and
-x^2 - y^2 - xy + 2x + 2y = -5

if we add these we get 0 = 0   so there are infinite solutions 

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