User ithisa - Mathematics Stack Exchange

31 votes

2 answers

35k views

Proof that the hypergeometric distribution with large $N$ approaches the binomial distribution.

asked Mar 14, 2013 at 19:17

18 votes

6 answers

26k views

Combinatorial proof of $\sum^{n}_{i=1}\binom{n}{i}i=n2^{n-1}$.

asked May 11, 2013 at 15:37

14 votes

1 answer

15k views

Show that triangle-free planar graphs are four-colorable

asked Jul 28, 2013 at 21:38

13 votes

5 answers

9k views

Deducing a probability distribution from its moment-generating function

asked Apr 7, 2013 at 0:12

11 votes

4 answers

3k views

Seating of $n$ people with tickets into $n+k$ chairs with 1st person taking a random seat

asked Jan 30, 2013 at 3:26

8 votes

4 answers

237 views

Contradiction in the rules regarding determinants and row operations?

asked Mar 21, 2013 at 17:56

8 votes

2 answers

1k views

Proving that a "prime graph" is connected

asked Aug 1, 2013 at 21:55

7 votes

4 answers

2k views

Is probability and the Law of Large Numbers a huge circular argument?

asked Aug 15, 2013 at 1:28

7 votes

1 answer

2k views

Proving that G contains a cycle with at least $k+1$ edges

asked Jul 1, 2013 at 14:40

6 votes

2 answers

2k views

Expectation score of multiple choice test

asked Mar 23, 2013 at 21:00

6 votes

2 answers

822 views

Interesting probability question about islands and bridges

asked Mar 23, 2013 at 21:45

6 votes

1 answer

1k views

What's so special about a 2D plane in graph theory?

asked Jul 17, 2013 at 0:37

5 votes

3 answers

360 views

Finding a planar graph satisfying these properties

asked Jul 18, 2013 at 21:25

5 votes

2 answers

11k views

Proving that similar matrices have identical ranks

asked Sep 9, 2013 at 23:27

5 votes

3 answers

128 views

No idea how to prove this property about symmetric matrices

asked Nov 16, 2013 at 20:52

5 votes

1 answer

365 views

Proving a property about Gauss-Seidel

asked Jun 11, 2015 at 16:10

5 votes

1 answer

258 views

Strange graph theory problem

asked Jul 10, 2013 at 18:58

5 votes

3 answers

5k views

Proving an identity with a combinatorial proof: $\binom{n}{k}\binom{k}{r}=\binom{n}{r}\binom{n-r}{k-r}$

asked May 11, 2013 at 14:43

5 votes

3 answers

260 views

Weird $3^n$ in an identity to be combinatorially proved

asked May 11, 2013 at 14:46

4 votes

2 answers

3k views

Biased random walk away from cliff

asked Apr 13, 2013 at 0:40

4 votes

2 answers

146 views

How does this "combinatorial proof" work?

asked May 7, 2013 at 21:56

4 votes

2 answers

2k views

Proof using natural deduction

asked Jun 3, 2013 at 18:13

4 votes

2 answers

13k views

Differentiating an infinite sum

asked Apr 5, 2013 at 14:21

4 votes

1 answer

2k views

Proving that a planar graph is bipartite [duplicate]

asked Jul 17, 2013 at 18:08

3 votes

2 answers

3k views

Proving a fact about 4-regular graphs

asked Aug 1, 2013 at 22:01

3 votes

2 answers

97 views

Completely baffled by this question involving putting matrices in matrices

asked Oct 29, 2013 at 18:00

3 votes

3 answers

5k views

Probability problem in textbook

asked Jan 15, 2013 at 19:44

3 votes

2 answers

187 views

Is this proof correct? Textbook has no solution.

asked Jan 19, 2013 at 22:25

3 votes

1 answer

232 views

Why was I wrong doing this problem?

asked Jan 26, 2013 at 18:41

3 votes

4 answers

535 views

Proving $q\Rightarrow r \models (p\land q) \Rightarrow (p \land r)$ using only natural deduction.

asked Jun 7, 2013 at 1:51

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99 Questions

Proof that the hypergeometric distribution with large $N$ approaches the binomial distribution.

Combinatorial proof of $\sum^{n}_{i=1}\binom{n}{i}i=n2^{n-1}$.

Show that triangle-free planar graphs are four-colorable

Deducing a probability distribution from its moment-generating function

Seating of $n$ people with tickets into $n+k$ chairs with 1st person taking a random seat

Contradiction in the rules regarding determinants and row operations?

Proving that a "prime graph" is connected

Is probability and the Law of Large Numbers a huge circular argument?

Proving that G contains a cycle with at least $k+1$ edges

Expectation score of multiple choice test

Interesting probability question about islands and bridges

What's so special about a 2D plane in graph theory?

Finding a planar graph satisfying these properties

Proving that similar matrices have identical ranks

No idea how to prove this property about symmetric matrices

Proving a property about Gauss-Seidel

Strange graph theory problem

Proving an identity with a combinatorial proof: $\binom{n}{k}\binom{k}{r}=\binom{n}{r}\binom{n-r}{k-r}$

Weird $3^n$ in an identity to be combinatorially proved

Biased random walk away from cliff

How does this "combinatorial proof" work?

Proof using natural deduction

Differentiating an infinite sum

Proving that a planar graph is bipartite [duplicate]

Proving a fact about 4-regular graphs

Completely baffled by this question involving putting matrices in matrices

Probability problem in textbook

Is this proof correct? Textbook has no solution.

Why was I wrong doing this problem?

Proving $q\Rightarrow r \models (p\land q) \Rightarrow (p \land r)$ using only natural deduction.