is $\exp \left( - 1 \over x^2 \right)$ differentiable  at $x=0$
8659
How do you show that $e^{-1/x^2}$ is differentiable at $0$?
142870
Prove the function is not differentiable at (0,0)
92399
Some questions about the function $xe^{-x}$
17452
Is differentiating on both sides of an equation allowed?
87743
Is a function whose derivative vanishes at rationals constant?
97553
Continuity of $\frac{2xy}{x^2+y^2}$ at $(0,0)$
119479
Derivative with respect to a 2-norm
31685
Differentiability of $f(x) = x^2 \sin{\frac{1}{x}}$ and $f'$
86860
Continuity of differentiable function $x^2\sin(1/x)$
80650
Complex differentiability of $f(z)=|z|$
117338
Counterexample to second derivative test when f''(x) is not continuously differentiable
143874
Limit of derivative is zero. Does it imply a limit for f(x)?
12726
Differentiating both sides of a non-differential equation
96112
Differentiating $ \left( 1 - \frac {1}{x} \right)^x $
39057
Check the differentiablity of $\theta :\mathbb R^2 \setminus\{(0,0)\}\to \mathbb R$
94193
determine whether $f(x, y) = \frac{xy^3}{x^2 + y^4}$ is differentiable at $(0, 0)$.
87131
Discontinuous at rationals and differentiable at irrationals?