Is $f$ differentiable?
49705
Is $f(x,y)=(x+2y+y^2+|xy|, 2x+y+x^2+|xy|)$ differentiable?
33130
$f$ differentiable except in $1$ point
25482
If a function is continuous and differentiable everywhere is the derivative continuous?
8321
Why differentiability implies continuity, but continuity does not imply differentiability?
55125
Continuous right derivative implies differentiability
143874
Limit of derivative is zero. Does it imply a limit for f(x)?
148737
Is $|xy|$ differentiable in $(0,0)$?
85623
Proof of continuity implied by differentiability
105068
Proving that the function is differentiable and $f'(0)=0$
120784
Differentiablility over closed intervals
147758
Differentiable but not continuously differentiable.
37850
Does the everywhere differentiability of $f$ imply it is absolutely continuous on a compact interval?
144323
Differentiation of a function
9270
Differentiable function, with $f'(x)=[f(x)]^2$
75932
Differentiability of $g:=f(\sqrt{x^2+y^2})$ for a $C^1$ function with $f'(0)=0$ NBHM $2008$
152877
Is a monotone differentiable function continuously differentiable?
83915
Showing that a function is not differentiable