Odpowiedź:
[tex]a)\\\\\begin{cases}2x+y=-1\\3x-y=-9\end{cases}\\\\\\\begin{cases}y=-1-2x\\3x-y=-9\end{cases}\\\\\\3x-(-1-2x)=-9\\\\3x+1+2x=-9\\\\5x=-9-1\\\\5x=-10\ \ /:5\\\\x=-2\\\\\\y=-1-2\cdot(-2)=-1+4=3\\\\\\\begin{cases}x=-2\\y=3\end{cases}[/tex]
[tex]b)\\\\\begin{cases}2x+y=7\\4x-y=-4\end{cases}\\\\\\\begin{cases}y=7-2x\\4x-y=-4\end{cases}\\\\\\4x-(7-2x)=-4\\\\4x-7+2x=-4\\\\6x=-4+7\\\\6x=3\ \ /:6\\\\x=\frac{3}{6}\\\\x=\frac{1}{2}\\\\\\y=7-\not2^1\cdot\frac{1}{\not2_{1}}=7-1=6\\\\\\\begin{cases}x=\frac{1}{2}\\y=6\end{cases}[/tex]
