#### Answer

Discontinuous for unit circle $x^{2}+y^{2}=1$

#### Work Step by Step

Use maple command to plot the graph of the function as depicted below:
From the above graph we observe that a circular break in the graph, which corresponds to unit circle for which function is discontinuous.
As function $f(x,y)=\frac{1}{1-x^{2}-y^{2}}$ is a rational function, it is continuous except where $1-x^{2}-y^{2}=0$
or $x^{2}+y^{2}=1$
Therefore,the function $f(x,y)=\frac{1}{1-x^{2}-y^{2}}$ is discontinuous for unit circle $x^{2}+y^{2}=1$