User Chris - Mathematics Stack Exchange

57 votes

1 answer

3k views

The $100$th derivative of $(x^2 + 1)/(x^3 - x)$

asked Aug 17, 2012 at 4:10

22 votes

6 answers

3k views

Intuition behind Cantor-Bernstein-Schröder

asked Oct 30, 2012 at 22:15

14 votes

1 answer

3k views

2012 Putnam Exam A3

asked Dec 4, 2012 at 4:49

14 votes

2 answers

695 views

1965 Putnam, B2

asked Sep 20, 2013 at 0:15

13 votes

1 answer

3k views

proof of l'Hôpital's rule [duplicate]

asked Aug 7, 2012 at 20:05

12 votes

3 answers

737 views

$\pi$, Dedekind cuts, trigonometric functions, area of a circle

asked Oct 20, 2012 at 2:57

10 votes

2 answers

6k views

isomorphism of Dedekind complete ordered fields

asked Jan 2, 2013 at 19:56

8 votes

3 answers

1k views

Even integer approximations to multiples of pi

asked Feb 19, 2013 at 22:14

8 votes

3 answers

2k views

Solving $x^p + y^p = p^z$ in positive integers $x,y,z$ and a prime $p$

asked Feb 24, 2014 at 23:19

8 votes

3 answers

278 views

Group of sphere transformations, impressing friends

asked Nov 17, 2012 at 0:05

8 votes

4 answers

12k views

Circle rotating within a circle (roulette)

asked Sep 17, 2014 at 23:52

7 votes

1 answer

342 views

Is this limit evaluation correct?

asked Jun 6, 2012 at 0:20

6 votes

6 answers

6k views

Verifying a proof that if $x,y,z \geq 0$ and $x+y+z = 1$, then $0 \le xy + yz + zx - 2xyz \le \frac{7}{27}$

asked Apr 27, 2013 at 22:08

6 votes

3 answers

360 views

If $\sum_{n=1}^\infty \frac{1}{a_n}$ converges, must $\sum_{n=1}^\infty \frac{n}{a_1 + \dots + a_n}$ converge?

asked Oct 15, 2014 at 17:01

6 votes

1 answer

176 views

If $A^n = I$, $n$ odd, $A$ a square integer matrix, does $A = I$?

asked Sep 13, 2014 at 17:19

5 votes

2 answers

2k views

Convergence of alternating nested radicals

asked Oct 20, 2013 at 20:10

5 votes

1 answer

264 views

Maximizing an unusual function (Putnam 1996)

asked May 23, 2013 at 2:27

5 votes

3 answers

1k views

correcting a mistake in Spivak [duplicate]

asked Apr 14, 2013 at 23:09

5 votes

1 answer

495 views

Find an autonomous differential equation with a given phase portrait

asked Feb 3, 2013 at 3:22

5 votes

3 answers

2k views

Why is arctangent smooth?

asked Jan 3, 2013 at 23:36

5 votes

1 answer

449 views

"Algorithmic" proofs in linear algebra

asked Oct 15, 2012 at 21:19

4 votes

2 answers

279 views

cardinality of $E^F$, $E, F = \emptyset$

asked Jun 23, 2012 at 3:43

4 votes

2 answers

3k views

set-theoretic function definition; recursion theorem

asked Apr 30, 2012 at 9:42

4 votes

2 answers

698 views

Polynomials $P(x)$ satisfying $P(2x-x^2) = (P(x))^2$

asked Sep 9, 2013 at 17:21

4 votes

1 answer

105 views

A neat application of Chebyshev's inequality

asked Oct 4, 2013 at 20:16

4 votes

0 answers

2k views

Iterations $n, n^n, (n^n)^{(n^n)},...$

asked Sep 14, 2014 at 15:38

3 votes

1 answer

113 views

If $I + A + \cdots + A^{n-1} = O$, $A$ a square integer matrix, $n$ odd, for what $k$ does $\det(\sum_{i = k}^{n-1} A^i) = \pm 1$?

asked Sep 13, 2014 at 19:33

3 votes

1 answer

108 views

Bounding the error in the finite difference approximation $\frac{-3f(x) + 4f(x+h) - f(x + 2h)}{2h} - f'(x)$

asked Dec 8, 2014 at 9:12

3 votes

0 answers

42 views

boundedness of signed measure $\mu$ with $\mu(A) < \infty$ for all $A$

asked Mar 27, 2017 at 4:41

3 votes

2 answers

190 views

Was sind und was sollen die compact spaces?

asked Apr 8, 2013 at 3:43

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48 Questions

The $100$th derivative of $(x^2 + 1)/(x^3 - x)$

Intuition behind Cantor-Bernstein-Schröder

2012 Putnam Exam A3

1965 Putnam, B2

proof of l'Hôpital's rule [duplicate]

$\pi$, Dedekind cuts, trigonometric functions, area of a circle

isomorphism of Dedekind complete ordered fields

Even integer approximations to multiples of pi

Solving $x^p + y^p = p^z$ in positive integers $x,y,z$ and a prime $p$

Group of sphere transformations, impressing friends

Circle rotating within a circle (roulette)

Is this limit evaluation correct?

Verifying a proof that if $x,y,z \geq 0$ and $x+y+z = 1$, then $0 \le xy + yz + zx - 2xyz \le \frac{7}{27}$

If $\sum_{n=1}^\infty \frac{1}{a_n}$ converges, must $\sum_{n=1}^\infty \frac{n}{a_1 + \dots + a_n}$ converge?

If $A^n = I$, $n$ odd, $A$ a square integer matrix, does $A = I$?

Convergence of alternating nested radicals

Maximizing an unusual function (Putnam 1996)

correcting a mistake in Spivak [duplicate]

Find an autonomous differential equation with a given phase portrait

Why is arctangent smooth?

"Algorithmic" proofs in linear algebra

cardinality of $E^F$, $E, F = \emptyset$

set-theoretic function definition; recursion theorem

Polynomials $P(x)$ satisfying $P(2x-x^2) = (P(x))^2$

A neat application of Chebyshev's inequality

Iterations $n, n^n, (n^n)^{(n^n)},...$

If $I + A + \cdots + A^{n-1} = O$, $A$ a square integer matrix, $n$ odd, for what $k$ does $\det(\sum_{i = k}^{n-1} A^i) = \pm 1$?

Bounding the error in the finite difference approximation $\frac{-3f(x) + 4f(x+h) - f(x + 2h)}{2h} - f'(x)$

boundedness of signed measure $\mu$ with $\mu(A) < \infty$ for all $A$

Was sind und was sollen die compact spaces?