Is $f(x,y)=\sqrt{|xy|}$ differentiable?
71260
Check differentiability of multivariable functions
115635
Differentiability of antiderivative and continuity of derivative
145173
$f: \mathbb{R}^2-\{0\} \rightarrow \mathbb{R}$ is continuously differentiable and $f(\alpha x) = \alpha^2f(x)$, then $x \cdot \nabla f(x) = 2 f(x)$
43956
Differentiating $f(x)^{g(x)}$
94193
determine whether $f(x, y) = \frac{xy^3}{x^2 + y^4}$ is differentiable at $(0, 0)$.
39995
Showing that partial derivatives of $f(x) = \frac{xy}{x^2+y^2}$ exist for $(x,y) \neq (0,0)$
122003
From the limit definition of differentiability, determine where the function $f(x) = \sqrt{x}$ is differentiable?
4636
How to show that $f$ is differentiable at $x=0.$
66560
Is a differentiable function always continuous?
30533
Showing that this function is infinitely differentiable
99984
Are polynomials infinitely many times differentiable?
105068
Proving that the function is differentiable and $f'(0)=0$
19828
Show that $\frac{x^3}{x^2+y^2}$ is not differentiable at $(0,0)$, even though all directional derivatives exist
849
$f$ differentiable, $f(x)$ rational if $x$ rational; $f(x)$ irrational if $x$ irrational. Is $f$ a linear function?
131357
Prove that $f(x,y)=xy$ is differentiable using the definition
57407
Show that $(x^2 + y^2) \sin\left(\frac{1}{x^2 + y^2}\right)$ is differentiable.
75932
Differentiability of $g:=f(\sqrt{x^2+y^2})$ for a $C^1$ function with $f'(0)=0$ NBHM $2008$