Can these two limits be used to directly check the twice differentiability of a function?
127125
Can the limit $\lim_{h \to 0}\frac{f(x + h) - 2f(x) + f(x - h)}{h^2}$ exist if $f'(x)$ does not exist at $x$?
100004
Differentiating $e^x$ from first principles using limits.
107203
Using Squeeze Theorem to show the following limits
131995
Two variables limit question
125615
Defining the derivative without limits
134721
A method for evaluating sums/discrete functions by assuming they can be made continuous and differentiable?
123790
Can we split the following limit?
135113
Is there a step by step checklist to check if a multivariable limit exists and find its value?
55268
Differentiable and Continuous functions on [0,1] with 'weird' conditions.
142490
Alternative proof for differentiability of inverse function?
11385
Using the Limit definition to find the derivative of $e^x$
117338
Counterexample to second derivative test when f''(x) is not continuously differentiable
67791
Can I exchange limit and differentiation for a sequence of smooth functions?
157728
When can you interchange composition of a limit?
55507
Multivariate differentiability verification
7945
Approximate $|x|$ with a smooth function
135199
Looking for a function $f$ that is $n$-differentiable, but $f^{(n)}$ is not continuous