In which points the function f r'ery f (x, y) = 12+ed; in those points, where this term is well-defined and when(x, y) # (0, 0) 0; (x, y) = (0, 0) is continuous? In which points the function is defined? If the function is continuous in the point (0, 0), prove it by using the definition of continuity at (0, 0). In this case the limit value at (0, 0) has to be proved by using the definition of the limit value. Calculate the partial derivative ay of (0, 0) and of ar (0, 0) by using the defini- tion of the partial derivative if it exists