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5
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Jan
22
comment $H,K$ be subgroups of a group $G$ such that $G$ is isomorphic with $H \times K$ ; then is $H$ normal in $G$ ?
@DanielFischer you're right, I didn't see it
Jan
21
answered $H,K$ be subgroups of a group $G$ such that $G$ is isomorphic with $H \times K$ ; then is $H$ normal in $G$ ?
Jan
20
revised What's wrong with this use of Taylor's expansions?
added 1 character in body
Jan
18
revised Series expansion of a function at infinity
big parentheses
Jan
18
suggested approved edit on Series expansion of a function at infinity
Jan
13
comment Calculating the centralizer of a matrix in a general linear group.
"the centralizer of $A$ in $\GL_n(3,\mathbb{R})$ is therefore the subgroup of invertible diagonal matrices." you mean that the union of all the centralizers is the regular diagonal subgroup or that every $A$ has the same centralizer?
Jan
12
comment Limit of real logarithm
Well the identity is just a consequence of the properties of the logarithm: you have $\ln(n) = \ln(\sqrt[n]{n} \sqrt[n]{n} \cdots \sqrt[n]{n}) = n\ln(\sqrt[n]{n})$ thus dividing both sides by $n$ we get $ln(\sqrt[n]{n}) = \frac1n \ln(n) $
Jan
9
revised What are some math concepts which were originally inspired by physics?
changed tags
Jan
9
suggested approved edit on What are some math concepts which were originally inspired by physics?
Jan
7
comment HOW do you refactor a recursive function into a single equation
Such answer. Much math. Wow. (kudos!)
Jan
7
accepted What's wrong with this use of Taylor's expansions?
Jan
7
comment What's wrong with this use of Taylor's expansions?
@Bort that's a really nice explanation
Jan
7
comment What's wrong with this use of Taylor's expansions?
now I understand the problem. If you add your last comment to your answer I'll be happy to accept it
Jan
7
comment What's wrong with this use of Taylor's expansions?
@GFR you're talking about the first expansion of $\sin x$? So I should go past $x^n$ with the Taylor expansion if $n$ is the power of the denominator?
Jan
7
comment What's wrong with this use of Taylor's expansions?
Yes, probably. But what's wrong in my attempt? Where's the error? If I didn't check on WA I wouldn't suspect it to be wrong, is such a nice result.
Jan
7
revised What's wrong with this use of Taylor's expansions?
added 1 character in body; deleted 2 characters in body; edited title
Jan
7
asked What's wrong with this use of Taylor's expansions?
Dec
31
comment V.I. Arnold says Russian students can't solve this problem, but American students can — why?
Calculus is a bit overkill for such a simple proof, see @Mick answer
Dec
28
accepted Are there automorphisms of $H$ which are not restriction of an automorphism of $G$?