Question 196661
x+y=4 or y=-x=4 (red line)
x-2y=1 or -2y=-x+1 or y=-x/-2+1/-2 or y=x/2-1/2 (green line)
{{{ graph( 300, 200, -6, 5, -10, 10, -x +4, x/2 -1/2) }}} (graph 300x200 pixels, x from -6 to 5, y from -10 to 10, of TWO functions -x +4 and x/2 -1/2). 
Ans. (3,1)
Proofs:
3+=4
3-2*1=1
3-2=1