Question

How do I solve 4x+y=0 and 5x-y=9

Answer 1

$\left \{ {{4x+Y=0} \atop {5x-Y=9}} \right.$
$(4x+y=0) + (5x-y=9) \\ 9x+y-y=0+9 \\ 9x=9$
$x=1$
$4(1)+y=0$
$y=-4$