lim of cos((x^2 + y^2) - 1)/(x^2 + y^2) as (x,y) approaches (0,0) I have no clue how to tackle this problem. I tried to find the level set so at least I can have a clue of what the graph looks like, but then, I didn't know how to find the level sets either. If I set c = the equation, I have 2 unknowns so I cannot solve, and its not an obvious graph like a circle or something. On the other hand, I tried l'hopitale but that needs the derivative and what in the world am i taking a derivative in terms of since there are 2 variables? I'm very confused. PLEASE HELP!