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I'm a student of mathematics in Germany.


Mar
21
comment Integration by substitution, derivative of $g ' (x)$, why?
If $F'(x) = f(x)$, then the derivative of $F(g(x))$ is $f(g(x))·g'(x)$, the identity you cited is false.
Mar
20
revised Show $f$ in Riemann integrable
deleted 1 characters in body
Mar
20
revised Show $f$ in Riemann integrable
added 52 characters in body
Mar
20
answered Show $f$ in Riemann integrable
Mar
18
comment Which math discipline should i learn to become familiar with rewriting equations?
Well, calculus.
Mar
18
comment Question about measure on set that is not in $\sigma$-algebra
Probably they mean “$μ_*(A) ≤ μ^* (A)$ and $μ_*(A) ≤ μ(A) ≤ μ^*(A)$ if $A ∈ \mathcal{A}$”.
Mar
18
comment Is every left maximal ideal the annihilator of a simple left module?
Ah, of course. Any primitive ideal is the intersection of maximal left ideals. That’s it. Thanks!
Mar
18
accepted Is every left maximal ideal the annihilator of a simple left module?
Mar
18
revised Is every left maximal ideal the annihilator of a simple left module?
marked the main question
Mar
18
asked Is every left maximal ideal the annihilator of a simple left module?
Mar
18
comment Showing that the sequence $z^n$ is normally but not uniformly convergent
@happymath You can’t (yet).
Mar
18
comment Showing that the sequence $z^n$ is normally but not uniformly convergent
Nevertheless, why is this downvoted? Okay, it’s a duplicate. But why is this downvoted?
Mar
18
comment Showing that the sequence $z^n$ is normally but not uniformly convergent
It’s not true. For $n ∈ ℕ$, choose $z = \sqrt[n]{2/3}$, then $|z^n - 0 |= 2/3 > ε$.
Mar
16
comment Question about lim sup
This was not the question, @NasuSama.
Mar
16
comment Group categories with only one object with a defined product
What do you mean by $\mbox {Mor}(\mathcal {G} ; \mathcal {G} ) = \mathcal {G}$? Oh, it seems this is edited and maybe it should be $\mbox {Mor}(G ; G) = \mathcal {G}$ or $… = G$ or something. It still doesn’t make sense to me: What do you want to say here?
Mar
16
comment Abstract algebra (Homomorphism)
Can you give your defintions of a ring and a ring homomorphism? Do you know any characterizations for injectivity? Do you know any examples of rings and maybe subrings?
Mar
16
comment Homework: prove there are two distinct integers $m$,$n$ such that $1/m+1/n$ is an integer.
The second one is preferable. Look at what you have done in your first attempt: You claimed “(1) is true, because (2) is false, because (1) holds as you can see by this example.” There’s a lot of redundancy. But not only that, you actually did go about this by saying: “Suppose (1) is false. Then (2) must be true. But (2) is false, because (1) holds as you can see by this example. And since (2) is false, (1) is true.” Just write: “(1) is true as you can see by this example.”
Mar
15
comment How can I complete this proof?
I haven’t looked through all of this, but let me upvote this for effort nonetheless. Seems legit.
Mar
15
comment The purpose to define open set in metric space
So you’ll end up with a discrete metric. But if you don’t give any context, it is hard to say what the purpose of such a metric is. Why are you even considering discrete metrics?
Mar
15
comment The purpose to define open set in metric space
A metric function is usually $X × X → ℝ_{≥0}$, do you mean for your metric to take values only in $ℤ^+$ (or maybe rather $ℤ_{≥ 0}$, since $d(x,x) = 0$ for all $x ∈ X$)?