X + y = 7 y + z = 5 z + x = - 4 Решите систему уравнений

Решите задачу:

$\left\{ \begin{aligned} x+y&=7\\ y+z & = 5\\ z+x&=-4.\\ \end{aligned} \right. $$ =\ \textgreater \ $$ \left\{ \begin{aligned} x+y&=7\\ y+z & = 5\\ -y+z&=-11.\\ \end{aligned} \right. $$ =\ \textgreater \ $$ \left\{ \begin{aligned} x+y&=7\\ y+z & = 5\\ 2z &=-6.\\ \end{aligned} \right. $$ =\ \textgreater \ $$ \left\{ \begin{aligned} x+y&=7\\ y+z & = 5\\ z=&=-3.\\ \end{aligned} \right.$

$=\ \textgreater \ $$ \left\{ \begin{aligned} x+y&=7\\ y & = 8\\ z&=-3.\\ \end{aligned} \right. $$ =\ \textgreater \ $$ \left\{ \begin{aligned} x&=-1\\ y & = 8\\ z&=-3.\\ \end{aligned} \right. $$$