How to show that a multivariable function is not differentiable?
40429
Differentiability of this picewise function
62581
What is an example that a function is differentiable but derivative is not Riemann integrable
102549
Check the differentiability of the given function.
62352
Proving a scalar function is differentiable at the origin but that its partial derivatives are not continuous at that point.
117338
Counterexample to second derivative test when f''(x) is not continuously differentiable
4636
How to show that $f$ is differentiable at $x=0.$
33130
$f$ differentiable except in $1$ point
144426
Example of a function $f:\mathbb{R}^2\to\mathbb{R}$ not differentiable at $(0,0)$, but has a directional derivative at $(0,0)$ in all directions
27775
Proving a function is not a contraction
146707
Formally show that the set of continuous functions is not measurable
107389
Show that the vector space of real functions is not finitely spanned
12726
Differentiating both sides of a non-differential equation
105068
Proving that the function is differentiable and $f'(0)=0$
5416
How does one prove if a multivariate function is constant?
49705
Is $f(x,y)=(x+2y+y^2+|xy|, 2x+y+x^2+|xy|)$ differentiable?
9924
Derivative of conjugate multivariate function
122957
Intuitive proof of multivariable changing of variables formula (jacobian) without using mapping and/or measure theory?