Question 245532
x+y=5
y=-x+5 (red line) 
x-y=7
-y=-x+7
y=x-7 (green line)
{{{ graph( 300, 200, -6, 10, -10, 10, -x +5, x -7) }}} (graph 300x200 pixels, x from -6 to 10, y from -10 to 10, of TWO functions -x +5 and x -7).