19,903 reputation
12238
bio website math.ntnu.no/~hanche
location Trondheim, Norway
age
visits member for 2 years, 10 months
seen 10 hours ago

Oct
20
comment Proof vector x + ⃗y = ⃗x + ⃗z then ⃗y = ⃗z
I didn't know about the Unicode character U+20D7 COMBINING RIGHT ARROW ABOVE until now. But you used it wrong: Combining characters have to go after the character you want to combine them with. It would be better to use LaTeX, though. (And in print, it usually works better to use boldface than an arrow above.)
Oct
20
comment Ladder against a wall.
@MarkBennet I had forgotten that one. I guess it's been a few decades since I had to solve a quartic.
Oct
20
comment Ladder against a wall.
The downvotes are piling up. And they're right: You haven't even asked a question, just stated that you find some equation difficult to solve. Is it the equation you want help with, or do you wonder if you have the right equation? I suppose you are aware that there is a formula for solving the general quartic, though it rather big and complicated. (And this one clearly has no rational roots.)
Oct
20
revised Ladder against a wall.
LaTeX
Oct
20
comment Connectedness of a set of complex numbers
Move $x$ from its original location to $1$ while keeping $xy=1$.
Oct
20
answered Connectedness of a set of complex numbers
Oct
19
comment Theorem of the convergence of the series of fourier!
Okay, I did that, then noticed that the question was closed as a duplicate. I wasn't too sure if the software would accept the edit under these circumstances, but it did. I won't edit it further, though.
Oct
19
revised Theorem of the convergence of the series of fourier!
Expand a bit more
Oct
19
comment Beautiful little number theory prob
Maybe try to find solutions to $u+v=uv$ first?
Oct
18
answered Proving commutativity
Oct
18
comment Theorem of the convergence of the series of fourier!
I'll give that answer a +1 for avoidance of the complex exponential function. If you do know the complex exponential, however, that is easier to understand.
Oct
18
revised Theorem of the convergence of the series of fourier!
A small bit more
Oct
18
revised Theorem of the convergence of the series of fourier!
Backslashify trig functions
Oct
18
comment Theorem of the convergence of the series of fourier!
No wonder you couldn't do it on your own. It is quite hard if you don't know the trick (see my answer).
Oct
18
answered Theorem of the convergence of the series of fourier!
Oct
18
comment What does a domain being maximal mean?
Yes, since any attempt to expand the domain takes you across the branch cut, where the function jumps to a different value. (This is possible to avoid, but then you have to leave the complex plane behind and work with Riemann surfaces. But that is a topic for a more advanced course, perhaps.)
Oct
18
comment Is $C(\Omega)$ a C*-algebra if $\Omega$ is not locally compact, nor compact?
That is correct. And that is all you need compactness for.
Oct
18
comment What does a domain being maximal mean?
If there is no analytic extension of the function to a larger domain than the given one, the given domain is maximal (for that function).
Oct
18
comment Is $C(\Omega)$ a C*-algebra if $\Omega$ is not locally compact, nor compact?
For one thing, if $C(\Omega)$ has unbounded members, what will you use for the norm on your C*-algebra? But the space of bounded continuous functions on $\Omega$ is always a C*-algebra. The proof is trivial.
Oct
18
comment Use contour integration to calculate real integrals
Along the left side, you have $z=-\epsilon+iu$, and so $dz=-idu$. But more importantly, $1/z=(-\epsilon-iu)/(u^2+\epsilon^2)$. You have left out the factor $-\epsilon-iu$, and made a similar omission along the right side.