Find a possible equation for the linear function $g(x,y)$ shown in the graph below 
Looking at the line passing through the origin, it looks like $g(x,y)=x-y-3$, because if $k=-3$, then $-3=0-0-3$, but this is not correct. Any help?

The suggested pattern is $g(x,y)=a(x-y)+b$ . Choose two points and compute $a$ and $b$.
You will find $a=-3$ and $b=-3$. Then $g(x,y)=-3(x-y+1)$
