12:56 AM
I was not sure - would fit here?
2

Let $\mathbb{R}_+ = [0, \infty)$. I'm looking for a family $\mathcal{U}$ of $2^\mathfrak{c}$ subsets of $\mathbb{R}_+$, such that any member of $\mathcal{U}$ is unbounded in $\mathbb{R}_+$, but the intersection of any two members of $\mathcal{U}$ is bounded. Does such family exists? It would als...

7 hours later…
8:03 AM
0

Occasionally we get a question of the form: "Look at this derivation/computation. Clearly, the result is wrong. Where is the mistake?" It is slightly different from typical solution-verification question. Namely here the OP knows that the solution is incorrect, so strictly speaking they do not a...

The above question was inspired by the following question. I added , but I was not sure whether some other tags would be suitable, too. I was considering .
6

Is something wrong with the calculation below?  \begin{align} \lim_{x \to \infty} \frac{4x^2}{x-2} &= \lim_{x \to \infty} \frac{4x}{1-2/x} \\ & = \frac{(\lim_{x \to \infty} 4x)}{(\lim_{x \to \infty} 1-2/x)} \\ & = \frac{(\lim_{x \to \infty} 4x)}{1} \\ & = \lim_{x \to \infty} 4x \\ & = \infty. ...

(BTW I noticed that question from HNQ list.)

15 hours later…
11:01 PM
0

Would it be useful to have tags for common proof-techniques? I thought about this when reading a question like this: how to strictly prove $\sin x<x$ for $0<x<\frac{\pi}{2}$. Lots of inequalities of this type can be proved by writing them as $f(x) \geq 0$ for $x \in [a,b]$ for some real valued s...