User Ivo Terek

86 votes

Why are two planes parallel to the same line not necessarily parallel?

answered May 10, 2015 at 23:20

85 votes

Accepted

What is the most unusual proof you know that $\sqrt{2}$ is irrational?

answered Jun 3, 2015 at 22:47

65 votes

Is there an "inverted" dot product?

answered Jan 17, 2018 at 1:55

35 votes

Creating a question that use the $\epsilon$-$\delta$ definition to prove that $f$ is a continuous function

answered Jul 2, 2014 at 20:44

34 votes

Accepted

Is hyperbolic rotation really a rotation?

answered Feb 26, 2018 at 23:58

32 votes

Accepted

Are all bilinear forms identically zero?

answered Sep 2, 2016 at 16:24

30 votes

A subset of a compact set is compact?

answered Jul 25, 2014 at 3:34

29 votes

Why must harmonic functions on compact Riemannian manifolds be constant?

answered Apr 22, 2020 at 15:43

27 votes

Accepted

Prove Or Disprove: tr(AB)=tr(A)*tr(B)

answered Jul 27, 2014 at 4:32

27 votes

Accepted

Explain "homotopy" to me

answered Feb 10, 2016 at 15:01

24 votes

Accepted

Prove that $\operatorname{trace}(A^TA) = 0\ \iff\ A = 0$.

answered Feb 18, 2015 at 16:44

21 votes

Nonobvious examples of metric spaces that do not work like $\mathbb{R}^n$

answered Dec 12, 2014 at 3:47

21 votes

Accepted

Does every non empty open set has measure greater than zero?

answered Mar 1, 2015 at 18:01

21 votes

Accepted

Are all measure zero sets measurable?

answered Jul 18, 2015 at 18:49

20 votes

How to prove that Lebesgue outer measure is translation invariant?

answered Aug 16, 2014 at 20:13

19 votes

Accepted

Why can partial derivatives be exchanged?

answered Mar 1, 2015 at 5:47

18 votes

Accepted

Why conjugate when switching order of inner product?

answered Jun 4, 2015 at 1:53

17 votes

Accepted

How to resize a vector to a specific length?

answered Aug 14, 2014 at 22:54

17 votes

Accepted

Find $f(2)$ if $f$ satisfies $2f(x)-3f(\frac1x)=x^2$

answered Feb 20, 2015 at 15:43

17 votes

Trace of AB = Trace of BA

answered Jun 6, 2015 at 5:09

17 votes

Proof that $\sqrt x$ is absolutely continuous.

answered Nov 23, 2015 at 19:50

16 votes

Accepted

How to find a 4D vector perpendicular to 3 other 4D vectors?

answered Aug 20, 2014 at 16:32

16 votes

Accepted

Lang's Linear Algebra: what's next?

answered Dec 20, 2014 at 21:58

16 votes

Which of the numbers $1, 2^{1/2}, 3^{1/3}, 4^{1/4}, 5^{1/5}, 6^{1/6} , 7^{1/7}$ is largest, and how to find out without calculator?

answered Jun 19, 2015 at 3:20

16 votes

Accepted

What is the meaning of expressions of the type $f(\cdot)$ (function (dot))?

answered May 17, 2015 at 16:31

16 votes

Accepted

Prove $x^TAx = 0$ $\implies$ A is skew-symmetric

answered Jan 23, 2016 at 19:46

15 votes

Intuition for the role of diffeomorphisms

answered Jun 17, 2019 at 20:29

15 votes

Accepted

Prove that Hölder condition in $\Bbb R^n$ implies continuity

answered Sep 16, 2014 at 0:58

15 votes

Accepted

What's the intuition behind the 2D rotation matrix?

answered Jun 30, 2014 at 19:38

15 votes

Accepted

Example of a metric space where Heine-Borel theorem does not hold

answered Oct 4, 2017 at 23:13

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2,094 Answers

Why are two planes parallel to the same line not necessarily parallel?

What is the most unusual proof you know that $\sqrt{2}$ is irrational?

Is there an "inverted" dot product?

Creating a question that use the $\epsilon$-$\delta$ definition to prove that $f$ is a continuous function

Is hyperbolic rotation really a rotation?

Are all bilinear forms identically zero?

A subset of a compact set is compact?

Why must harmonic functions on compact Riemannian manifolds be constant?

Prove Or Disprove: tr(AB)=tr(A)*tr(B)

Explain "homotopy" to me

Prove that $\operatorname{trace}(A^TA) = 0\ \iff\ A = 0$.

Nonobvious examples of metric spaces that do not work like $\mathbb{R}^n$

Does every non empty open set has measure greater than zero?

Are all measure zero sets measurable?

How to prove that Lebesgue outer measure is translation invariant?

Why can partial derivatives be exchanged?

Why conjugate when switching order of inner product?

How to resize a vector to a specific length?

Find $f(2)$ if $f$ satisfies $2f(x)-3f(\frac1x)=x^2$

Trace of AB = Trace of BA

Proof that $\sqrt x$ is absolutely continuous.

How to find a 4D vector perpendicular to 3 other 4D vectors?

Lang's Linear Algebra: what's next?

Which of the numbers $1, 2^{1/2}, 3^{1/3}, 4^{1/4}, 5^{1/5}, 6^{1/6} , 7^{1/7}$ is largest, and how to find out without calculator?

What is the meaning of expressions of the type $f(\cdot)$ (function (dot))?

Prove $x^TAx = 0$ $\implies$ A is skew-symmetric

Intuition for the role of diffeomorphisms

Prove that Hölder condition in $\Bbb R^n$ implies continuity

What's the intuition behind the 2D rotation matrix?

Example of a metric space where Heine-Borel theorem does not hold