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1d
answered What is the relationship between the trace/norm of a quaternion and the definition in field theory?
Aug
23
comment Defining a partial order on $A\times B$, given partial orders on $A$ and on $B$
What is the problem in following the definition?
Aug
22
comment Show that sum of divisors of a composite number $n$ is $> n+ \sqrt{n}$
You already did
Aug
22
comment Show that sum of divisors of a composite number $n$ is $> n+ \sqrt{n}$
Is $n$ a divisor of $n$? Must be, or else the assertion is false (take $n=4$). Hence .....
Aug
20
comment How to find a 4D vector perpendicular to 3 other 4D vectors?
Well, of course you can define a $4$-dimensional cross-product by mimicking the usual (3-D) definition. The point is how to compute it quickly.
Aug
20
answered How to find a 4D vector perpendicular to 3 other 4D vectors?
Aug
20
comment An epimorphism from $\mathbb Z⊕\mathbb Z⊕\cdots$ to $\mathbb Q$
Right, but he's exactly asking for the construction .....
Aug
20
comment An epimorphism from $\mathbb Z⊕\mathbb Z⊕\cdots$ to $\mathbb Q$
The OP's asking for a map of additive groups, I suppose.
Aug
20
comment An epimorphism from $\mathbb Z⊕\mathbb Z⊕\cdots$ to $\mathbb Q$
How do you get, say, $\frac12$?
Aug
20
answered An epimorphism from $\mathbb Z⊕\mathbb Z⊕\cdots$ to $\mathbb Q$
Aug
20
answered If $p\mid|G|$ then how many elements of order $p$ are there in $G$?
Aug
19
comment Disprove the statement given below
It is true if $x\neq0$, but $x=0$ gives the obvious counterexample in Squirtle's answer
Aug
19
comment Induced group action: homology vs cohomology
Mind that going from a space to its dual, group actions go from left-actions to right-actions and viceversa. When the group acts by involutions the two should be basically the same, though. (Because elements coincide with their inverses)
Aug
15
answered Show that $K:=\left\{z\in\mathbb{C}: \lvert z\rvert =1\right\}$ is a topological group.
Aug
15
answered Show that $\mathbb{F}_p^\times \simeq \text{Aut}(\mathbb{F}_p^+) $ holds
Aug
4
awarded  Yearling
Jul
30
answered Proving that $E=F\oplus G$ for two given subspaces of $E = \mathbb R^3$
Jul
29
comment Why do we still do symbolic math?
Why constructing real numbers (and complex numbers, and $p$-adic numbers, and so on and so forth ...) if all actual computations involve approximations with rationals only? Because it is FUN !!
Jul
29
comment Notation for vectors that exclude zero
$(a_1,..,a_n)\in(K^\times)^n$ where $K$ is the coefficient field, is another possibility.
Jul
29
answered Can you have a nontrivial automorphism of an elliptic curve $E/S$ which when restricted to a geometric fiber is the identity?