user avatar
user avatar
user avatar
Per Manne
  • Member for 10 years
  • Last seen this week
  • Bergen, Norway
120 votes

Find five positive integers whose reciprocals sum to $1$

60 votes

Why does $\tan^{-1}(1)+\tan^{-1}(2)+\tan^{-1}(3)=\pi$?

56 votes
Accepted

What is the integral of 1/x?

43 votes
Accepted

What do we lose passing from the reals to the complex numbers?

38 votes
Accepted

The graph of xy = 1 is connected or not

35 votes

Can't argue with success? Looking for "bad math" that "gets away with it"

20 votes

Father and daughter river crossing puzzle.

18 votes
Accepted

Prove that $A=\left(\begin{array}{ccc}1&2&3\\4&5&6\\7&8&9\end{array}\right)$ is not invertible

18 votes

Disproving the claim that the numbers 1+2+4, 1+2+4+8, 1+2+4+8+16... alternate between prime and composite

17 votes

Examples of mathematical results discovered "late"

16 votes
Accepted

Motivation of Vieta's transformation

14 votes
Accepted

Are infinitesimals dangerous?

13 votes
Accepted

A couple of formulas for $\pi$

11 votes

History of Dual Spaces and Linear Functionals

10 votes
Accepted

What is the probability of this exact same Champions League draw?

9 votes

closure, convex hull and closed convex hull

8 votes
Accepted

What cubic problems did Tartaglia and Fior pose to each other?

8 votes

Did Leonardo of Pisa prove $n=4$ case of FLT?

8 votes

Tricks to Intuitively See Uniform Continuity

8 votes
Accepted

Is the Riemann sphere homeomorphic to $\overline{\mathbb{R}}\times\overline{\mathbb{R}}$?

7 votes

Notation problem in integration: write $dx$ or ${\mathrm{d}}x$?

7 votes
Accepted

Is this limit equal to 1?

7 votes

A function which is in $L^1$ but does not belong to $L^\infty$

7 votes

Which simple puzzles have fooled professional mathematicians?

7 votes

History of $f \circ g$

7 votes
Accepted

Geometric proof that $\left|\frac{i-z}{i+z}\right|<1$ for $z\in \mathbb{H}$

7 votes
Accepted

The 'abelian group' custom

7 votes

What are some conceptualizations that work in mathematics but are not strictly true?

6 votes
Accepted

Needing an example of one riemann integrable function

6 votes
Accepted

How many chess games of a suspect does one have to analyze to have a reliable answer to the question whether the suspect cheats?

1
2 3 4 5
7