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Harald Hanche-Olsen
  • Member for 10 years, 6 months
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155 votes
Accepted

How do I convince my students that the choice of variable of integration is irrelevant?

65 votes
Accepted

If $e^A$ and $e^B$ commute, do $A$ and $B$ commute?

49 votes

Self-Contained Proof that $\sum\limits_{n=1}^{\infty} \frac1{n^p}$ Converges for $p > 1$

44 votes

Of any 52 integers, two can be found whose difference of squares is divisible by 100

42 votes
Accepted

Matrix raised to 14th power

33 votes

Why Do The Axioms of Euclidean Geometry Not Need To Include the Definition of Space?

31 votes

Can there be a function that's even and odd at the same time?

29 votes

An example for a calculation where imaginary numbers are used but don't occur in the question or the solution.

25 votes
Accepted

How many times are the hands of a clock at $90$ degrees.

25 votes

I need a proof that a line cannot intersect a circle at three distinct points

22 votes

Difference between supremum and maximum

21 votes

$C^*$-algebra which is also a Hilbert space?

21 votes
Accepted

A problem of J. E. Littlewood

19 votes

Convergence of $\sum_{n=1}^\infty{\left(\sqrt[n]{n}-1\right)}$

19 votes

What are the differences between differential and gradient?

18 votes

How to show $\int_{0}^\infty e^{x^2}dx$ does not converge?

17 votes
Accepted

Is there an explanation why the reflection of $f(x)$ through y = x is its inverse?

17 votes
Accepted

Is the closure of connected set path connected?

16 votes
Accepted

What is convex combination of two points?

16 votes
Accepted

If $\sum\limits_{n=1}^\infty na_n$ converges , does $\sum\limits_{n=1}^\infty na_{n+1}$ converge?

15 votes
Accepted

Discontinuities of the derivative of a differentiable function on closed interval

15 votes

Is product of Banach spaces a Banach space?

14 votes

Showing $ \sum_{n=0}^{\infty} \frac{1}{(3n+1)(3n+2)}=\frac{\pi}{3\sqrt{3}}$

14 votes
Accepted

Why is every selfadjoint operator closed?

13 votes
Accepted

Find the characteristic polynomial of the inverse of a matrix

13 votes
Accepted

Difference of asymptotes at infinity

13 votes
Accepted

Point on the left or right side of a plane in 3D space

12 votes
Accepted

Can this intuition give a proof that an isometry $f:X \to X$ is surjective for compact metric space $X$?

12 votes

An intuitive idea about fundamental group of $\mathbb{RP}^2$

12 votes

What is the importance of determinants in linear algebra?

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