Reputation
919
Top tag
Next privilege 1,000 Rep.
Create new tags
Badges
1 8 29
Impact
~40k people reached

1d
awarded  Famous Question
Aug
21
comment Prove or disprove: a closed, non-open set is also bounded
@Bernard that may be true, but I think it depends on the author. My book uses the limit point definition. Incidentally I think it's much more fascinating to define two concepts separately and then prove that they're related. E.g. define $\ln(x)$ as an integral and $\exp(x)$ as a summation, then prove that they're inverse functions (rather than defining one as the inverse of the other).
Aug
20
comment Prove or disprove: a closed, non-open set is also bounded
a set is closed iff it contains all its limit points
Aug
20
comment Prove or disprove: a closed, non-open set is also bounded
Good answer; the only thing that would make me happier is if you used the definition of closed to prove it is closed. (Not that proving its complement is open isn't a valid proof, but I like a more direct approach.)
Aug
20
comment Prove or disprove: a closed, non-open set is also bounded
@NigelOvermars WolframAlpha says the right end is open. But it does contain all its limit points…
Aug
20
asked Prove or disprove: a closed, non-open set is also bounded
Aug
8
revised Why $\int \frac{dx}{\sqrt{9-x^2}} = sin^{-1}\frac{x}{3}$?
removed blockquotes
Aug
8
suggested approved edit on Why $\int \frac{dx}{\sqrt{9-x^2}} = sin^{-1}\frac{x}{3}$?
Aug
3
comment Are the Real numbers really Complete?
@MarkS. — very interesting. any links to further reading on this?
Aug
2
revised How many ways are there to define sine and cosine?
formatting and spelling
Aug
2
comment The relation x=1
… and thus $x=y$. That last part is key for antisymmetry.
Aug
2
suggested approved edit on How many ways are there to define sine and cosine?
Aug
2
comment The number $\sum\limits_{n=-\infty}^{\infty} \frac{1}{2^{n^2}}$ is transcendental
The title of this question should be more explicit. How about, "Is there a direct proof that the number … is trancendental?"
Jul
28
comment Is Belnap's four valued-logic a boolean algebra?
duplicate of math.stackexchange.com/questions/1354050/…
Jul
28
revised What is the definition of a Critical Point?
title change and formatting
Jul
28
suggested approved edit on What is the definition of a Critical Point?
Jul
28
comment What is the domain of $f(x)=\frac{1}{x}-\frac{1}{x}$?
Right. $a-a = 0$, for all real numbers $a$. If $a$ isn't a real number, all bets are off.
Jul
15
comment Why is $e^{\pi \sqrt{163}}$ almost an integer?
@Strants — I'm not saying it can't be answered, I'm just saying "almost" is relative. By that logic, you could argue 10 is "almost" equal to 100 (compared to, for example, $-10^{100}$). And because "almost" is relative, it's not a very good question to ask on math.SE.
Jul
15
comment Can I have a logical explanation for why this number is so ridiculously close to a whole number?
@AAron — understandable. You might want to read "How do I ask a good question?" and "What topics can I ask about here?".
Jul
15
comment Why is $e^{\pi \sqrt{163}}$ almost an integer?
similar question: "can you explain why $2+\sqrt[3]{\frac{1}{e^{10\pi}}}$ is almost-but-not-quite an integer?"