17,386 reputation
43365
bio website mai.liu.se/~halun
location Linköping, Sweden
age 44
visits member for 4 years, 2 months
seen 4 hours ago

I liked this site better in the good old days when the questions were fewer and more interesting... I still drop in from time to time, though.


8h
comment Continuous function at [-1,1] not differentiable at infinite points at [-1,1].
(Picky remark: There are no infinite points in $[-1,1]$, or in the whole set of real numbers for that matter. But there are infinitely many...)
13h
revised How to prove the left limit and the right limit?
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20h
answered Inviscid Burger's equation solution
21h
comment How integrate $ \iint_{D} (\frac{x^2}{x^2+y^2})dA, \ \ \ \ D: x^2+y^2=a^2 \ \ and \ \ x^2+y^2=b^2, \ \ 0<a<b $
If you actually have equalities, then you're integrating over the empty set, so the integral is trivially zero!
21h
comment How integrate $ \iint_{D} (\frac{x^2}{x^2+y^2})dA, \ \ \ \ D: x^2+y^2=a^2 \ \ and \ \ x^2+y^2=b^2, \ \ 0<a<b $
You're missing a factor of 1/2, right?
22h
comment How integrate $ \iint_{D} (\frac{x^2}{x^2+y^2})dA, \ \ \ \ D: x^2+y^2=a^2 \ \ and \ \ x^2+y^2=b^2, \ \ 0<a<b $
Do you really mean $=a^2$ and $=b^2$? Inequalities would look less strange...
1d
comment what is the limit of this special linear function?
Neither do I. Anyway, it's a perfectly valid question to ask, and it also shows the importance of having a precise definition to fall back upon in cases where one's intuition is insufficient. (I have no idea if your book gives the precise definition, but judging from its title, I suspect that it doesn't...) You can read it on Wikipedia, for example.
1d
comment what is the limit of this special linear function?
Cool down! You might want to edit this question into a less angry tone, unless you want to attract downvotes. From what you write, it looks like you had the same question closed earlier, and in that case it's probably because people felt that you didn't provide enough context. How did this question arise? What are your own thoughts? (Too many people just post their homework questions verbatim on this site, and that's why many users here are a bit "allergic" to questions that don't show any signs of effort from the person asking.)
1d
revised what is the limit of this special linear function?
edited tags
1d
answered what is the limit of this special linear function?
2d
comment How to show that : If $\int x^n f(x) dx = 0$ for all $n$ then $f(x) = 0$ for all $x$
This question is very strange. For an indefinite integral, it doesn't even make sense to require that it's zero, since it is only determined up to an additive constant anyway.
Oct
26
answered Good books written by great mathematicians
Oct
26
comment A question about diffrentiability and integrablity
en.wikipedia.org/wiki/Volterra%27s_function
Oct
26
comment Why is the following equivalent transformation of the imaginary number legitimate?
See also here: math.stackexchange.com/questions/44406/…
Oct
26
comment Transformations from n-sphere coordinates to cartesian coordinates.
Well, let's see... Yes, I found the one that I had in mind: "Separation of variables on n-dimensional Riemannian manifolds. I. The $n$-sphere $S_n$ and Euclidean $n$-space $R_n$", J. Math. Phys., 1986.
Oct
26
comment Are there functions for which the cyclic integration-by-parts technique does not work?
Try $\int \cos x \cos x \, dx$.
Oct
26
comment Question about $i$
In step (2), I guess you meant $\sqrt[4]{i^4}$ rather than $\sqrt[4]{i}$.
Oct
26
answered Transformations from n-sphere coordinates to cartesian coordinates.
Oct
26
revised Clifford algebra - Gamma matrices
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Oct
25
revised Proving the relation: $∇(\mathbf{u}·\mathbf{v})=(\mathbf{v}·∇)\mathbf{u}+(\mathbf{u}·∇)\mathbf{v}+\mathbf{v}×(∇×\mathbf{u})+\mathbf{u}×(∇×\mathbf{v})$
edited tags