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• ㄱ.$\displaystyle \lim _ {(x, y) \rightarrow (0, 0)} {} \frac{xy} {\sqrt {x ^ {2} +y ^ {2}}} =0$
• ㄴ.$\displaystyle \lim _ {(x, y) \rightarrow (0, 0)} {} \frac{xy ^ {2}} {x ^ {2} +y ^ {4}} =0$
• ㄷ.$\displaystyle \lim _ {(x, y) \rightarrow (0, 0)} {} \frac{\sin (xy)} {\left | x \right | + \left | y \right |} =0$