Is $\sqrt {f(x)}$ infinitely differentiable?
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?
15032
Let $f: \Bbb R \to \Bbb R$ be a differentiable function such that $\sup_{x \in \Bbb R}|f'(x)| \lt \infty$. Then
9270
Differentiable function, with $f'(x)=[f(x)]^2$
117906
Show that $\liminf\limits_{x\to \infty}|f'(x)|=0$ if $\lim\limits_{x\to \infty}f(x)/x=0$ and $f$ is differentiable
75932
Differentiability of $g:=f(\sqrt{x^2+y^2})$ for a $C^1$ function with $f'(0)=0$ NBHM $2008$
94193
determine whether $f(x, y) = \frac{xy^3}{x^2 + y^4}$ is differentiable at $(0, 0)$.
68752
A few questions about infinite derivative.
28297
derivative of x^x^x... to infinity?
69378
The derivative of $x!$ and its continuity
87743
Is a function whose derivative vanishes at rationals constant?
143491
Show that $f$ is differentiable on $(−1, 1)$.
13150
If the derivative of $f$ is never zero, then $f$ is one-to-one
135199
Looking for a function $f$ that is $n$-differentiable, but $f^{(n)}$ is not continuous
96547
Is $|z|^2$ complex differentiable?
4636
How to show that $f$ is differentiable at $x=0.$
84785
Is $f(x)=x+\frac{x}{x+1}$ uniformly continuous on $(0,\infty)$
138864
If $f\colon \mathbb{R} \to \mathbb{R}$ is such that $f(x+y)=f(x)f(y)$ and $f'(0)$ exists, then $f$ is differentiable on $\mathbb R$