User Derek Allums

26 votes

Research done by high-school students

answered Jul 23, 2012 at 15:58

8 votes

Accepted

Determining if the transformation $(x_1,x_2,x_3)\mapsto(2x_2,x_2+2,2x_2)$ is linear or not

answered Jul 8, 2016 at 18:30

7 votes

Accepted

Is there an operational isomorphism from $(\mathbb{Z},+)$ to $(\mathbb{Q}^{+},\cdot)$?

answered May 24, 2012 at 17:57

6 votes

What's $R[x]/(x^2)$ isomorphic to?

answered Aug 12, 2014 at 2:59

5 votes

Short exact sequences of modules.

answered Nov 24, 2013 at 22:12

4 votes

Accepted

How to determine m for which $f(x)$ is surjective?

answered May 26, 2012 at 13:16

4 votes

Accepted

Min/Max of $f(x,y) = e^{xy}$ where $x^3+y^3=16$

answered May 20, 2012 at 11:47

4 votes

Isomorphism $k[x,y]/(y-x^2)$ onto $k[x]$

answered Jul 28, 2012 at 14:30

3 votes

Accepted

Example of a non-affine irreducible scheme

answered Jun 30, 2013 at 13:19

3 votes

Accepted

Prove that there is a constant $c$ for which $f(x) = cx$ for all $x \in \mathbb{Q}$

answered Apr 9, 2016 at 1:43

3 votes

Accepted

Proving this bilinear form is non degenerate if and only if $f$ is surjective?

answered Aug 15, 2016 at 16:15

3 votes

Accepted

let $\mathscr{F}$ be a field and let $\pi:\mathbb{C}[x] \to\mathscr{F}$ be a surjective ring homomorphism. Prove that $\mathscr{F}\cong\mathbb{C}$

answered Jun 7, 2023 at 6:45

2 votes

Accepted

The kernel of a homomorphism at the end of an exact sequence

answered Sep 18, 2023 at 6:58

2 votes

Accepted

Expected Number of Flips and Probability in a Coin Toss Experiment

answered May 15 at 9:05

2 votes

Prove that the number of pairs in a string starting and ending with $1$ is $\frac{m(m-1)}{2}$

answered Jan 10, 2020 at 12:33

2 votes

Accepted

Definition of $Z/\left<n\right>$

answered Oct 21, 2020 at 6:00

2 votes

Quadric surface as a $\mathbb{F}_n$ surface

answered Feb 1, 2014 at 20:06

2 votes

Accepted

Determinant of matrix composition

answered May 20, 2012 at 3:40

2 votes

What's the fundamental group of $E^2\setminus Q^2$

answered May 19, 2013 at 12:47

2 votes

Holomorphic function on the unit disk $f$, show the set $z,w\in \mathbb{C}$ such that $f(z)=f(w)$ is not countable

answered Jan 8, 2013 at 18:20

2 votes

Does the inequality $|\sin(x)|\leq |x|$ extend to the complex numbers?

answered Jun 22, 2012 at 16:18

1 vote

Accepted

A Gröbner Basis Computation Gone Bad

answered Jul 18, 2012 at 15:47

1 vote

$P(X \cap Y) \ge P(X) + P(Y) - 1$?

answered May 20, 2012 at 15:39

1 vote

Bounded function in $[0,1]$ that does not attain its supremum and infimum.

answered May 28, 2012 at 17:17

1 vote

Meaning of equations in a presentation of a group

answered May 29, 2012 at 0:16

1 vote

Van Kampen's Theorem with Torus and Projective Plane

answered Apr 27, 2013 at 21:21

1 vote

Accepted

Least Squares Fitting - Logarithmic

answered Aug 13, 2012 at 1:26

1 vote

Tensor Book Recommendation Request

answered Jul 5, 2013 at 21:51

1 vote

Accepted

Different way showing a subgroup is a subgroup of another subgroup

answered May 24, 2014 at 19:45

1 vote

Accepted

How to tell that $W$ is a subspace of $ \mathbb R^3$?

answered Feb 7, 2016 at 16:33

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50 Answers

Research done by high-school students

Determining if the transformation $(x_1,x_2,x_3)\mapsto(2x_2,x_2+2,2x_2)$ is linear or not

Is there an operational isomorphism from $(\mathbb{Z},+)$ to $(\mathbb{Q}^{+},\cdot)$?

What's $R[x]/(x^2)$ isomorphic to?

Short exact sequences of modules.

How to determine m for which $f(x)$ is surjective?

Min/Max of $f(x,y) = e^{xy}$ where $x^3+y^3=16$

Isomorphism $k[x,y]/(y-x^2)$ onto $k[x]$

Example of a non-affine irreducible scheme

Prove that there is a constant $c$ for which $f(x) = cx$ for all $x \in \mathbb{Q}$

Proving this bilinear form is non degenerate if and only if $f$ is surjective?

let $\mathscr{F}$ be a field and let $\pi:\mathbb{C}[x] \to\mathscr{F}$ be a surjective ring homomorphism. Prove that $\mathscr{F}\cong\mathbb{C}$

The kernel of a homomorphism at the end of an exact sequence

Expected Number of Flips and Probability in a Coin Toss Experiment

Prove that the number of pairs in a string starting and ending with $1$ is $\frac{m(m-1)}{2}$

Definition of $Z/\left<n\right>$

Quadric surface as a $\mathbb{F}_n$ surface

Determinant of matrix composition

What's the fundamental group of $E^2\setminus Q^2$

Holomorphic function on the unit disk $f$, show the set $z,w\in \mathbb{C}$ such that $f(z)=f(w)$ is not countable

Does the inequality $|\sin(x)|\leq |x|$ extend to the complex numbers?

A Gröbner Basis Computation Gone Bad

$P(X \cap Y) \ge P(X) + P(Y) - 1$?

Bounded function in $[0,1]$ that does not attain its supremum and infimum.

Meaning of equations in a presentation of a group

Van Kampen's Theorem with Torus and Projective Plane

Least Squares Fitting - Logarithmic

Tensor Book Recommendation Request

Different way showing a subgroup is a subgroup of another subgroup

How to tell that $W$ is a subspace of $ \mathbb R^3$?