Limit of (1-xy)/(1+xy) as (x,y) approaches (1,-1)

[Wesleytf]

Homework Statement

\frac{lim}{(x,y)->(1,-1)} \frac{1-xy}{1+xy}

Homework Equations

none

The Attempt at a Solution

I know from the graph this limit doesn't exist, but I tried subbing y=-x, xy=u, y=-1, x=1, and I always come up with the limit going to infinity. Not sure what I'm doing wrong, but I feel like I'm close.

 

[Dick]

I'm not sure what your question is. Isn't 'going to infinity' one way that a 'limit doesn't exist'?