How to prove this function isn't differentiable at origin
112859
$f(x,y) = \frac{x^3y}{x^4 + y^2}$ is not differentiable at $(0,0)$.
85092
Proving $ f(x) = x^2 $ is not uniformly continuous on the real line
128524
Proving there is no analytic function
3518
Proving $f(x)=1/x$ on $(0,1 )$ is not uniformly continuous
38923
What can we say about differentiability of $f$ at $c$?
61486
Show that $f$ is not differentiable at $(0,0)$ - $\frac{x_1^2x_2}{x_1^2+x_2^2}$
135199
Looking for a function $f$ that is $n$-differentiable, but $f^{(n)}$ is not continuous
3978
How can you prove that a function has no closed form integral?
18825
Integrable but not differentiable function
127538
Show $f(x)=x\ln x$ is not uniformly continuous
82001
How to prove the function is a constant
6417
Can a function be differentiable at the end points of its (closed interval) domain?
130322
Show that $f(x) = 0$ if $x = 0$ $f(x) = \text{exp}(-1/x^{2})$ if $x \neq 0$ is infinitely differentiable but not analytic at $x_{0} = 0$ `
134122
When is differentiating an equation valid?
148737
Is $|xy|$ differentiable in $(0,0)$?
124346
Where is $f(z)=\Re (z)$ differentiable?
27933
Show that unit circle is not homeomorphic to the real line