[tex] \begin{cases}-(x-3)+2(y+1)=8\\3x+y=12\end{cases}\\\\\begin{cases}-(x-3)+2(y+1)=8\\3 y=-3x+12\end{cases}\\\\ \begin{cases}- x+3+2( -3x+12+1)=8\\ y=-3x+12\end{cases}\\\\ \begin{cases}- x+3 -6x+24+2=8\\ y=-3x+12\end{cases}\\ \\\begin{cases}- 7x+29=8\\ y=-3x+12\end{cases} \\\\\begin{cases}-7x=8-29\\ y=-3x+12\end{cases} \\\\\begin{cases}-7x=-21\ \ |:(-7)|\\ y=-3x+12\end{cases}\\\\\begin{cases} x= 3\\ y=-3*3+12\end{cases}\\\\\begin{cases} x= 3\\ y=3\end{cases}[/tex]
[tex]sprawdzenie:\\\\ \begin{cases}-(3-3)+2(3+1)=8\\3*3+3=12\end{cases}\\\\ \begin{cases}0+2*4=8\\9+3=12\end{cases}\\\\\begin{cases}8=8\\12=12\end{cases}\\\\ L=P [/tex]