108,031 reputation
591207
bio website
location
age
visits member for 3 years, 7 months
seen 47 mins ago

45m
comment How can I find fifth root of unity?
Are you still here, Nora?
47m
comment Trace of a certain matrix
I've never seen my name mangled that badly. But: how many eigenvalues does that matrix have? What must they be? What do they add up to? What's the relation between eigenvalues and trace?
53m
comment Proof of a sum of positive divisors
If you get it, write it up, and post it as an answer, please.
58m
comment Proof of a sum of positive divisors
You can factor any integer into powers of different primes, and then evaluate $f$ as the product of its values on the prime powers.
1h
comment Proof of a sum of positive divisors
When a function is multiplicative, it is completely determined by its values on prime powers.
1h
comment Proof of a sum of positive divisors
Isn't it the case that both sides are multiplicative functions? so all you have to do is prove it in the case where $n$ is a prime power?
3h
comment Trace of a certain matrix
If the eigenvalues are not required to be in ${\bf Z}_{227}$, then I don't see how one can answer this question.
3h
comment Why null space and column space?
I think you mean "null space and column space of a matrix," Justin.
3h
comment Shortest distance from a point to vertices of a cube
I think you've written $O(p)$ where you meant $O(d)$.
6h
comment Anti-symmetric relation given by a matrix
I take it the ones represent pairs in the relation, and the zeros represent pairs not in the relation. So $(2,3)$ and $(3,2)$ are not in the relation.
6h
comment Proof of taking derivatives of both equal sides
"at any point $(a,b,c)$" doesn't make sense if $f$ is a function of 2 variables. How do you evaluate $f(x,y)$ at $(a,b,c)$?
12h
comment Know eigenvalues, get $Q$ of $A=QLQ'$
The vector $(1/7)(2,4,5)$ does not have norm 1.
12h
comment Check if the angle is constructable
Well, do you know the cosine of 30 degrees? and is it a constructable number? Better yet: do you know how to construct an equilateral triangle? and how to bisect an angle? The formula for $\cos3\theta$ is really overkill, if all you're interested in is 30 degrees.
15h
comment solve this congruence please.
The congruence I wrote down implies the left side is odd, so $6-n$ is odd, so $n$ is odd. When $n$ is odd, $7^n\equiv-1\pmod4$, so we need $6-n\equiv3\pmod4$.
1d
comment How to show that the vertices of a convex hull are given by these specific subsets…
Asking it here is fine BUT only if you link it to the MO post so people here can benefit from what was written there (and so people here won't waste your time by telling you things you were already told there).
1d
comment How can I have a copy of this old paper?
Funny, it got an answer on MO, mathoverflow.net/questions/185045/…
1d
comment How to show that the vertices of a convex hull are given by these specific subsets…
Previously posted to MO, mathoverflow.net/questions/185009/… where it got closed but did attract some comments.
1d
comment Solving a Complex Number polynomial problem
The last equation you have written down is certainly nonsense.
1d
comment How can I find fifth root of unity?
You're gooing to have a hard time proving $1+a^2+a^3+a^4=0$. You'll have better luck with $1+a+a^2+a^3+a^4=0$.
1d
comment solve this congruence please.
$7^n(6-n)\equiv1\pmod4$, $n$ must be 3 modulo 4.