Answer :
[tex] \left \{ {{4x+Y=0} \atop {5x-Y=9}} \right. [/tex]
[tex](4x+y=0) + (5x-y=9) \\ 9x+y-y=0+9 \\ 9x=9[/tex]
[tex] x=1[/tex]
[tex]4(1)+y=0[/tex]
[tex]y=-4[/tex]
[tex](4x+y=0) + (5x-y=9) \\ 9x+y-y=0+9 \\ 9x=9[/tex]
[tex] x=1[/tex]
[tex]4(1)+y=0[/tex]
[tex]y=-4[/tex]
