TITLE: Computing Limits
# !b2 Problem:
Find the following limit
> ;
                                       x - y
                        lim          ------------
                       x,y -> (3,4)    2    2 1/2
                                     (x  + y )

# !b3 Solution:
The function is continuous at (3,4) so computing the limit is just
a matter of evaluating the function at (3,4).
> f := (x,y) -> (x-y)/sqrt(x^2+y^2):
> `f(3,4)` = f(3,4);
                                 f(3,4) = -1/5


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