User Watson - Mathematics Stack Exchange

35 votes

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Non-abelian group with infinitely many abelian subgroups

answered Jun 16, 2016 at 16:58

25 votes

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Do there exist numbers normal in every base except for one?

answered Sep 25, 2016 at 12:15

21 votes

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How do you simplify this square root of sum: $\sqrt{7+4\sqrt3}$?

answered Jun 16, 2016 at 13:06

20 votes

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Call a number "holy" if it contains no $666$ in its decimal expansion. Are there infinitely many holy powers of $2$?

answered Sep 29, 2019 at 11:12

19 votes

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Would this solution of the limit of the sequence be correct?

answered Feb 2, 2016 at 14:05

17 votes

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A field extension of degree 2 is a Normal Extension.

answered Feb 8, 2016 at 16:29

16 votes

How prove this inequality??

answered Dec 28, 2015 at 13:47

16 votes

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Are the plane and the third dimensional space homeomorphic?

answered Oct 26, 2016 at 11:41

15 votes

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Existence of at least one inert prime

answered Jun 11, 2018 at 14:58

12 votes

Why is $ (2+\sqrt{3})^n+(2-\sqrt{3})^n$ an integer?

answered Aug 25, 2016 at 10:40

11 votes

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What is the order of $ab$ in an abelian group?

answered Aug 25, 2016 at 12:28

11 votes

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Find the two values of $k$ for which $2x^3-9x^2+12x-k$ has a double real root.

answered Feb 2, 2016 at 19:59

11 votes

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Prove that every bilinear map can be written as a sum of bilinear symmetric map and a bilinear anti-symmetric map.

answered Feb 5, 2017 at 15:50

10 votes

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Does $R[[x]] \cong S[[x]]$ imply $R\cong S$

answered May 11, 2018 at 12:17

10 votes

Interesting and unexpected applications of $\pi$

answered Feb 8, 2016 at 20:24

10 votes

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Is there a continuous function such that $\int_0^{\infty} f(x)dx$ converges, yet $\lim_{x\rightarrow \infty}f(x) \ne 0$?

answered Mar 4, 2016 at 21:05

10 votes

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Prove that if $n \in \mathbb{Z}[\sqrt{2}]$ has an even norm, then $\sqrt{2} \mid n$

answered Feb 18, 2016 at 22:37

8 votes

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Express the ideal $(6) \subset\mathbb Z\left[\sqrt {-5}\right]$ as a product of prime ideals.

answered Sep 5, 2016 at 18:29

8 votes

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Abelian Galois group of $f$ implies splitting is simple extensions by a root of $f$.

answered May 9, 2016 at 17:58

8 votes

Does the commutator group of $S_n$ equal $A_n$ in general?

answered Jun 22, 2016 at 12:32

8 votes

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Determinant of a matrix $P$ such that $AP=BP$.

answered Sep 3, 2016 at 12:22

8 votes

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Problem with inequality: $ \left| \sqrt{2}-\frac{p}{q} \right| > \frac{1}{3q^2}$

answered Feb 14, 2016 at 20:42

8 votes

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Let $d\in \mathbb Q$ , to prove $\mathbb Q(\sqrt d) \subseteq \mathbb Q(e^{2i\pi/n})$ for some positive integer $n$ (without Kronecker-Weber)

answered Apr 21, 2017 at 16:49

8 votes

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Alternative form of Eisenstein integers

answered Jan 14, 2017 at 16:52

7 votes

Accepted

Prove linear combinations of logarithms of primes over $\mathbb{Q}$ is independent

answered Feb 8, 2017 at 10:58

7 votes

What is the characteristic of p-adic number fields?

answered Jun 5, 2018 at 12:28

7 votes

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A question on Hartshorne Chapter III Proposition 2.6

answered Nov 7, 2018 at 19:40

7 votes

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Countable ordinal

answered Feb 10, 2016 at 14:44

7 votes

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Is any subgroup normal?

answered Sep 18, 2016 at 10:13

7 votes

Does there always exist an irreducible polynomial of degree $d$ over $\mathbb{Z}/p\mathbb{Z}$?

answered Jul 25, 2016 at 17:56

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299 Answers

Non-abelian group with infinitely many abelian subgroups

Do there exist numbers normal in every base except for one?

How do you simplify this square root of sum: $\sqrt{7+4\sqrt3}$?

Call a number "holy" if it contains no $666$ in its decimal expansion. Are there infinitely many holy powers of $2$?

Would this solution of the limit of the sequence be correct?

A field extension of degree 2 is a Normal Extension.

How prove this inequality??

Are the plane and the third dimensional space homeomorphic?

Existence of at least one inert prime

Why is $ (2+\sqrt{3})^n+(2-\sqrt{3})^n$ an integer?

What is the order of $ab$ in an abelian group?

Find the two values of $k$ for which $2x^3-9x^2+12x-k$ has a double real root.

Prove that every bilinear map can be written as a sum of bilinear symmetric map and a bilinear anti-symmetric map.

Does $R[[x]] \cong S[[x]]$ imply $R\cong S$

Interesting and unexpected applications of $\pi$

Is there a continuous function such that $\int_0^{\infty} f(x)dx$ converges, yet $\lim_{x\rightarrow \infty}f(x) \ne 0$?

Prove that if $n \in \mathbb{Z}[\sqrt{2}]$ has an even norm, then $\sqrt{2} \mid n$

Express the ideal $(6) \subset\mathbb Z\left[\sqrt {-5}\right]$ as a product of prime ideals.

Abelian Galois group of $f$ implies splitting is simple extensions by a root of $f$.

Does the commutator group of $S_n$ equal $A_n$ in general?

Determinant of a matrix $P$ such that $AP=BP$.

Problem with inequality: $ \left| \sqrt{2}-\frac{p}{q} \right| > \frac{1}{3q^2}$

Let $d\in \mathbb Q$ , to prove $\mathbb Q(\sqrt d) \subseteq \mathbb Q(e^{2i\pi/n})$ for some positive integer $n$ (without Kronecker-Weber)

Alternative form of Eisenstein integers

Prove linear combinations of logarithms of primes over $\mathbb{Q}$ is independent

What is the characteristic of p-adic number fields?

A question on Hartshorne Chapter III Proposition 2.6

Countable ordinal

Is any subgroup normal?

Does there always exist an irreducible polynomial of degree $d$ over $\mathbb{Z}/p\mathbb{Z}$?