<PRE><B>Question 333867</B>
x+y= -1
y=-x-1 red line
2x-y=4
-y=-2x+4
y=2x-4 green line
Create a graph by saying 
{{{ graph( 300, 200, -6, 5, -10, 10, -x -1, 2x -4) }}} (graph 300x200 pixels, x from -6 to 5, y from -10 to 10, of TWO functions -x -1 and 2x -4). 
Solution (1,-2).
Proofs:
-2=-1-1
-2=-2 
-------------
-2=2*1-4
-2=2-4
-2=-2</PRE>