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 Tumbleweed
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Apr
12
comment Give a bijection
For Q: I assume that you have already shown a bijection between Z and Q. Use that. This can be written quite neatly using the Calkin-Wilf sequence. The negative rationals are unchanged, 0 -> 1, and otherwise $q\to\frac{1}{2\lfloor q\rfloor - q + 1}$.
Mar
27
comment Picking points on a sphere at random
This was investigated by the inimitable Kevin S. Brown here
Mar
18
answered simple question on probability…
Mar
10
comment A five-digit number whose square has its last five digits equal to the number.
Can you find a one digit number whose last digit is equal to the number? A two digit number?
Mar
3
comment Using percentages to apply fisher's exact test
As the counts become large Fisher's exact test becomes a Chi-Squared test.
Feb
23
answered Proving Gale-Shapley algorithm completes in $O(n^2)$
Feb
22
comment Consider the divides-relationship on $A =\{1, 2, 3, 4, 6\}$. Use the notation $D(x, y)$ to mean $x$ divides $y$.
for example 2 divides 4, 1 divides 6.
Feb
20
comment Simplify $ \tan \{{1\over2}\tan^{-1}x + \tan^{-1}y\} $ .
Try using an identity for $\tan(a + b)$
Feb
8
comment Measurable Subsets
What are bounds on $\sum |E_j \cap S_n|$?
Feb
7
answered Finding $P(A \cap D)$ when $P(A), P(B), P(C), P(D), P(A \cap B), P(A \cap D) + P(B \cap C)$ is known
Feb
5
comment Finding $P(A \cap D)$ when $P(A), P(B), P(C), P(D), P(A \cap B), P(A \cap D) + P(B \cap C)$ is known
Draw the simplest Venn diagram that has nontrivial values for the above, and see what you can manipulate while keeping the values constant.
Jan
31
comment can we find a $k_4$ colored with 1 color in a $k_8$ which is colored with just 2 colors?
What is the minimum size of a set of edges such that each $K_4$ contains at least one edge in the set?
Jan
28
awarded  Tumbleweed
Jan
21
asked Induced subgraphs of a hypercube
Jan
20
comment How can I tell which one of these numbers is greater?
Your sum is less than 9E99 times $(9E99)^9$. This should give you a start
Jan
14
comment Spivak's Limit Example
Pay close attention to the difference between < and $\le$ in the definition. Understand that $0<|x-a|$ means that $x\ne a$. (This is going to continue to be important in analysis.)
Jan
10
revised How was the expression relating two general solutions to $x\frac{\partial u}{\partial x}+2\frac{\partial u}{\partial y}- 2u = 0$ obtained?
added 212 characters in body
Jan
10
answered How was the expression relating two general solutions to $x\frac{\partial u}{\partial x}+2\frac{\partial u}{\partial y}- 2u = 0$ obtained?
Jan
10
comment Continuity at a point.
Are you sure it is true for all $m$ and $n$? Hint: $x^3$ is odd.
Jan
10
comment How was the expression relating two general solutions to $x\frac{\partial u}{\partial x}+2\frac{\partial u}{\partial y}- 2u = 0$ obtained?
Equate the two solutions.