Differentiability of the function:$g(x,y)=f(\sqrt{x^2+y^2})$
75932
Differentiability of $g:=f(\sqrt{x^2+y^2})$ for a $C^1$ function with $f'(0)=0$ NBHM $2008$
153942
Solution of functional equation $f(x+y)=f(x)+f(y)+y\sqrt{f(x)}$
127449
Uniform continuous of $f(x,y) = \sin(x^2+y)$
158681
How to show that $e^x$ is differentiable?
73073
Differentiating $y=x^{2}$
59956
Show that the function $g(x) = x^2 \sin(\frac{1}{x}) ,(g(0) = 0)$ is everywhere differentiable and that $g′(0) = 0$
80650
Complex differentiability of $f(z)=|z|$
9270
Differentiable function, with $f'(x)=[f(x)]^2$
126461
Show that $g:I\to\mathbb{R}$ is continuous and $f:(x-x_0)g(x)$ is differentiable
105319
A calculus problem with functions such that $f''(x) = g(x)$ and $g''(x) = f(x)$
124346
Where is $f(z)=\Re (z)$ differentiable?
5419
Continuous functions with $f^2(x)=g^2(x)\neq 0$
96022
Symmetry of second derivative - Sufficiency of twice-differentiability
59279
Example of function that is differentiable, but the second derivative is not defined
148737
Is $|xy|$ differentiable in $(0,0)$?
2506
twice differentiable functions
85480
Let $f(x,y)=\frac{x^3-y^3}{x^2+y^2}$. Is f differentiable in $(0,0)$?