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J. J.'s user avatar
J. J.'s user avatar
J. J.'s user avatar
J. J.
  • Member for 13 years, 6 months
  • Last seen more than a week ago
  • Finland
59 votes

Are cyclic groups always abelian?

41 votes

Geometry problem involving infinite number of circles

26 votes

Is the determinant differentiable?

22 votes

How do you calculate this limit $\mathop {\lim }\limits_{x \to 0} \frac{{\sin (\sin x)}}{x}$?

21 votes
Accepted

3 random numbers to describe point on a sphere

16 votes
Accepted

All functions $\frac{1}{f\left(y^2f(x)\right)} = \big(f(x)\big)^2\left(\frac{1}{f\left(x^2-y^2\right)} + \frac{2x^2}{f(y)}\right)$

16 votes
Accepted

What is the importance of 3n in the Collatz Conjecture?

16 votes

Alternative proof of simple integral inequality

13 votes

Non-closed subspace of a Banach space

13 votes
Accepted

Why isn't the volume of a sphere $ π^2r^3?$

12 votes

Number of surjections from $\{1,...,m\}$ to $\{1,...,n\}$

11 votes

Proving that none of these elements 11, 111, 1111, 11111...can be a perfect square

10 votes

Does absolute convergence of a sum imply uniform convergence?

10 votes

How to prove that: $\sqrt{25!+3} \in \mathbb{R}\setminus\mathbb{Q}$

10 votes

Prove that the two integrals are equal with periodic function

10 votes

Is $e^{\sqrt{2}}\gt 3$ or $e^{\sqrt{2}}\lt 3$

9 votes
Accepted

$ x+y = 1 $ and $ \frac{1}{x} + \frac{1}{y} = 1 $ Solve $ x^3 + y^3 $

9 votes

Finding every $n$ such that $a_n$ is an integer

9 votes

Limits involving factorials $\lim_{N\to\infty} \frac{N!}{(N-k)!N^{k}}$

9 votes
Accepted

Orthogonal Projection

8 votes
Accepted

Convergence of $a_n=(1/2)^{(1/3)^{...^{(1/n)}}}$

8 votes
Accepted

Lines covering points on napkin

7 votes

Is it possible to find square root using only rational numbers and elementary arithmetic operators

7 votes
Accepted

Smooth functions for which $f(x)$ is rational if and only if $x$ is rational

7 votes
Accepted

Detecting if a decimal is terminal or not?

7 votes

Condition for Fourier series

7 votes

What is the cardinality of the group of bijections from $\Omega$ to $\Omega$ with finite support?

6 votes

How can I calculate the limit $\lim_{x\to-2}\frac{\tan (\pi \cdot x)}{(x+2)}$ without l'Hopital?

6 votes
Accepted

Is it possible to have a mixed parentage of 10% 90%

6 votes
Accepted

Point reflection across a line

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