Let \(f\left( {x,y} \right) = \;\left\{ {\begin{array}{*{20}{c}} {\frac{{xy}}{{\sqrt {{x^2} + {y^2}} }}\;\;\;{x^2} + {y^2} \ne 0}\\ {0\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;x = y = 0} \end{array}} \right.\), Then Which of the following is not Correct ?
1
f(x, y) is not differentiable at the origin
2
f(x, y) is continuous at the origin
3
fx (0,0) = f(0,0)
4
fy (0,0) = f(0,0)