Is $f$ differentiable in $0$?
61486
Show that $f$ is not differentiable at $(0,0)$ - $\frac{x_1^2x_2}{x_1^2+x_2^2}$
35671
Why can a discontinuous function not be differentiable?
94193
determine whether $f(x, y) = \frac{xy^3}{x^2 + y^4}$ is differentiable at $(0, 0)$.
143874
Limit of derivative is zero. Does it imply a limit for f(x)?
49587
Does a differentiable everywhere function have a continuous derivative?
71260
Check differentiability of multivariable functions
24900
Homogeneity and Differentiability at $0$ implies linearity?
46398
Is $(x^2+y^2+z^2) \ \sin \frac{1}{\sqrt{x^2+y^2+z^2}}$ Differentiable in $(0,0,0)$?
80650
Complex differentiability of $f(z)=|z|$
130748
Infinitely differentiable function with given zero set?
10564
$f$ be a smooth function on real line , $f(0)=0$ , $f(x)>0, \forall x \ne 0$ and any $f^{(n)}(0)=0$ ; is $\sqrt f$ smooth?
8659
How do you show that $e^{-1/x^2}$ is differentiable at $0$?
142870
Prove the function is not differentiable at (0,0)
112859
$f(x,y) = \frac{x^3y}{x^4 + y^2}$ is not differentiable at $(0,0)$.
34136
$f$ is differentiable in $[0,1]$ ,$\sup_{x\in[0,1]}|f'(x)| \le M\lt+\infty $
31051
Is $f(x,y)=(xy)^{2/3}$ differentiable at $(0,0)$?
119042
If $f+g$ and $f$ are differentiable at $a$, must $g$ be differentiable at $a$?