A)[latex] \left \{ {{y=-3x} \atop {5x + 3y = 12}} \right. [/latex]

Действительное решение нет [x,y] ∈∅

[latex] \left \{ {{y=-3x} \atop {5x + 3y = 12}} \right. \ \ \ \ \ \left \{ {{y=-3x} \atop {5x + 3*(-3x) = 12}} \right. \ \ \ \ \ \ \left \{ {{y=-3x} \atop {5x -9x = 12}} \right. \\ \left \{ {{y=-3x} \atop {-4x = 12}} \right. \ \ \ \ \ \ \ \left \{ {{y=-3x} \atop {x =-3}} \right. \ \ \ \ \ \ \ \ \ \left \{ {{y=-3*(-3)} \atop {x =-3}} \right. \ \ \ \ \ \ \ \left \{ {{y=9} \atop {x =-3}} \right. [/latex] ответ: (-3;9)