2.7.60 Function Properties

Condition: explore the function \ (f \) for continuity and differentiation at the point \ ((0; 0) \). \ [f (x, y) = \ left \ {\ begin {array} {c} \ tan \ frac {x} {\ sqrt {x^{2}+y^{2}}}}, \ quad x^}+y^{2 \\ 0, \ quad X^{2}+y^{2} = 0 \ End {Array} \ Right. \]