$\text{A.}\{\begin{array}{l}x-y=2\\ 2x+y=13\end{array}$  

$\{\begin{array}{l}5-3=2\\ 2\cdot 5+3=13\end{array}$  

$\text{B.}\{\begin{array}{l}6+x-y=8\\ 5-3x+2y=-4\end{array}$ $\text{B.}\{\begin{array}{l}6+x-y=8\\ 5-3x+2y=-4\end{array}$  

$\{\begin{array}{l}6+5-3\stackrel{?}{=}8\\ 5-3\cdot 5+2\cdot 3\stackrel{?}{=}-4\end{array}$  

$\{\begin{array}{l}11-3=8\\ 5-15+6\stackrel{?}{=}-4\end{array}$    

$\{\begin{array}{l}11-3=8\\ -10+6=-4\end{array}$  

$\text{C.}\{\begin{array}{l}1-x-y=5\\ 7+4x=y-1\end{array}$

$\{\begin{array}{l}1-5-3\stackrel{?}{=}5\\ 7+4\cdot 5\stackrel{?}{=}5-1\end{array}$  

$\{\begin{array}{l}1-8\ne 5\\ 7+20\ne 4\end{array}$  

Podany układ równań nie jest spełniony dla pary liczb (5,3).

$\text{D.}\{\begin{array}{l}-5=x-y-7\\ 8+y=-x+16\end{array}$  

$\{\begin{array}{l}-5\stackrel{?}{=}5-3-7\\ 8+3\stackrel{?}{=}-5+16\end{array}$  

$\{\begin{array}{l}-5=5-10\\ 11=-5+16\end{array}$