The function given is \( f(x, y)=\left\{\begin{array}{l}\frac{x^{2}-y^{2}}{x^{2}+y^{2}} \text { if }(x, y) \neq(0,0) \text {; } \\ 0 \text { if }(x, y)=(0,0) .\end{array}\right. \)
This function is defined piecewise, with a specific definition at the point
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