Answer
Answers may vary. One system of equations is
$x+y=1$
$x-y=-1$
Work Step by Step
Green line: $x+y=1$
Purple line: $x-y=-1$
$x-y=-1$
$x=y-1$
$x+y=1$
$(y-1)+y=1$
$2y-1=1$
$2y=2$
$2y/2=2/2$
$y=1$
$x=y-1$
$x=1-1$
$x=0$
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