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41m
revised Can critical point that $f''$ has different sign in its every neighborhood be a local extreme point?
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43m
comment Can critical point that $f''$ has different sign in its every neighborhood be a local extreme point?
@zhw Good point though. I'll add a picture of $f$ itself.
47m
comment Can critical point that $f''$ has different sign in its every neighborhood be a local extreme point?
@zhw Yes, $0$ is. $f(0)$ is $0$, while for all other $x$, $f(x)$ is positive, as explained. So $0$ is a global minimum (and therefore local minimum.) Meanwhile, the function you proposed is not 2nd differentiable at $0$.
1h
revised Can critical point that $f''$ has different sign in its every neighborhood be a local extreme point?
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1h
revised Can critical point that $f''$ has different sign in its every neighborhood be a local extreme point?
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2h
revised Can critical point that $f''$ has different sign in its every neighborhood be a local extreme point?
added 350 characters in body
2h
revised Can critical point that $f''$ has different sign in its every neighborhood be a local extreme point?
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2h
answered Can critical point that $f''$ has different sign in its every neighborhood be a local extreme point?
1d
comment Homework 8th grader: $\pi^2$ is irrational
Maybe. But my other suggestion is that it is intentionally too hard for that level. It could just be trying to get students to think hard for the logical exercise of it all. There is value in that even if the answer to the question ends up being inaccessible to the readers.
1d
answered Homework 8th grader: $\pi^2$ is irrational
May
21
comment What do the symbols $\mathbb{Z}$ and $\mathbb{Z}_n$ mean on this discrete math problem?
@CameronWilliams It's just a comment. Zev has it covered.
May
21
comment What do the symbols $\mathbb{Z}$ and $\mathbb{Z}_n$ mean on this discrete math problem?
$\mathbb{Z}$ stands for Zahlen.
May
20
revised How to find inverse of generator of a finite field?
added 11 characters in body
May
19
awarded  Yearling
May
18
comment Is $(A-A^{-1})$ skew-symmetric?
I don't understand your first equals sign. $(A-A^{-1})^T=A^T-(A^{-1})^T=A^T-A$, not $A-A^T$.
May
18
answered Solve $|1 + x| < 1$
May
17
answered Notation $E[t^X]$ where $X$ is a random variable
May
17
awarded  integration
May
16
comment Multiply vector by number that rescales to integers - what is the name?
Aka the least common denominator.
May
16
answered Solve the equation $\log_{2} x \log_{3} x = \log_{4} x$