Question 144937
1) x-y=1
-Y=-X+1
Y=X-1 (RED LINE)    
3x+y=7
Y=-3X+7 (GREEN LINE)
{{{ graph( 300, 200, -6, 5, -10, 10, x -1, -3x +7) }}} (graph 300x200 pixels, x from -6 to 5, y from -10 to 10, of TWO functions x -1 and -3x +7). 
ANSWER (2,1)
2) 2x-y=1
-y=-2x+1
y=2x-1 (red line)
3y=6x-3
y=6x/3-3/3
y=2x-1 (green line)
{{{ graph( 300, 200, -6, 5, -10, 10, 2x -1, 2x -1) }}} (graph 300x200 pixels, x from -6 to 5, y from -10 to 10, of TWO functions 2x -1 and 2x -1).
NO UNIQUE SOLUTION AS THESE 2 EQUATIONS ARE EQUAL WITH 2 UNKNOWS.