## Search found 21 matches

Mon Dec 17, 2012 7:57 am UTC
Topic: 1148: "Nothing to Offer"
Replies: 93
Views: 24162

### Re: 1148: "Nothing to Offer"

Djehutynakht wrote:Would anyone like to offer an explanation as to this one.

http://en.wikipedia.org/wiki/Blood,_toi ... _and_sweat
Mon Nov 26, 2012 12:05 pm UTC
Topic: 1139: "Rubber and Glue"
Replies: 55
Views: 28696

### Re: 1139: "Rubber and Glue"

BlitzGirl wrote:Who's the girl on top of the swing set? BHG's future girlfriend?

She doesn't have something to cut/remove the ropes of the swing set, so I'm not sure it's her
Mon Apr 23, 2012 3:05 pm UTC
Topic: 1045: "Constraints"
Replies: 86
Views: 43144

### Re: 1045: Constraints

Relevant to the comic subject :

http://en.wikipedia.org/wiki/Oulipo
Sun Sep 18, 2011 8:06 pm UTC
Forum: Mathematics
Topic: Help with a simple proof
Replies: 27
Views: 2424

### Re: Help with a simple proof

You don't need induction.

Try to calcul [imath]I_n - aI_{n-1}[/imath]
Sat Sep 17, 2011 8:49 pm UTC
Forum: Mathematics
Topic: Arithmetic recreation with Fermat
Replies: 5
Views: 1457

### Re: Arithmetic recreation with Fermat

The assertion "the equality 2^k=u^n+v^n (2) which is impossible for n>2 and u, v, k, n positive integers" is wrong.

Counter-examples : 2^(n+1) = 2^n + 2^n and (more general) 2^(an+1) = (2^a)^n + (2^a)^n
Thu Sep 08, 2011 4:23 am UTC
Forum: Mathematics
Topic: Ten repeating numbers in Pi
Replies: 21
Views: 7205

### Re: Ten repeating numbers in Pi

Erm, not really. Does 0.101010101... have a sequence of 10 digits that repeat? Of course, 0101010101 (and 1010101010 ) is a sequence of 10 digits that repeat in 0.101010101... it's a bad counter exemple :mrgreen: But I see where there is a place for interpretation in "find a group of n digits ...
Thu Sep 08, 2011 3:09 am UTC
Forum: Mathematics
Topic: Ten repeating numbers in Pi
Replies: 21
Views: 7205

### Re: Ten repeating numbers in Pi

So I ask the Math board, are there any ten numbers in Pi that repeat? And if so where could I locate them? Yes, there are 10 digits of pi that repeat (every infinite number has at least a sequence of 10 digits that repeat, try understand why ;)), but to locate it you must make an extensive research...
Fri Sep 02, 2011 1:16 pm UTC
Forum: Mathematics
Topic: Lucky 13
Replies: 7
Views: 1727

### Re: Lucky 13

You can study the equation (x+y)² - x*y² +1 = 0 (you'll also need to study the equation (x+y)² - x*y² -1 = 0): (1-x)y² + (2x)y + (1+x²) = 0 It's a 2nd degree polinomial in y, \Delta = 4x^2-4(1-x)(1+x^2) = 4x^3+4x-4 For x>=1, delta is > 0, and we have : y = \frac{-2x \pm 2\sqrt{x^3+x-...
Fri Sep 02, 2011 12:13 pm UTC
Forum: Fictional Science
Topic: "Laser blasters."
Replies: 52
Views: 7224

### Re: "Laser blasters."

Actually, that's 43 tons, not kilotons. 1 gram antimatter annihilating with 1 gram of matter, would be 43kt (and 1.8*1014 J), 1 milligram would be just 43 tons. Although the equivalent of 43 tons of TNT is still quite a bit of energy.

Powers of ten are nasty
Fri Sep 02, 2011 11:09 am UTC
Forum: Fictional Science
Topic: "Laser blasters."
Replies: 52
Views: 7224

### Re: "Laser blasters."

Also, with only 1mg of matter reacted, you would already have released 1.8e11J, more than enough to blow up the brick, increasing the rate of reaction. Just for comparaison, 1.8e11J the energy released by the explosion of 43 kiloton of TNT, and the nuclear bomb dropped on Hiroshima was only 15 kilo...
Fri Sep 02, 2011 10:28 am UTC
Forum: Science
Topic: Net linear momentum from rotating bodies
Replies: 14
Views: 2347

### Re: Net linear momentum from rotating bodies

this is what i suspected, obviously, exactly because it isn't used for space propulsion, what i can't get my head around is why.

Because the momentum in a closed system is conserved : the center of mass of the system stay motionless.
Fri Sep 02, 2011 8:59 am UTC
Forum: Books
Topic: Author's Politics, or do you care what an author thinks?
Replies: 31
Views: 8614

### Re: Author's Politics, or do you care what an author thinks?

A good exemple of a talented writer with nauseous political views is Céline

http://en.wikipedia.org/wiki/Louis-Ferdinand_C%C3%A9line
Fri Sep 02, 2011 8:39 am UTC
Forum: Mathematics
Topic: Multiplication or the summation operator (sigma)
Replies: 28
Views: 4459

### Re: Multiplication or the summation operator (sigma)

dissonant wrote:
[imath]\ln\left(\prod x_n \right) = \sum \ln\left( x_n \right)[/imath]

Actually it's not exactly true

Spoiler:
every [imath]x_n[/imath] need to be positive
Fri Sep 02, 2011 4:05 am UTC
Forum: Science
Topic: Projectile angle such that distance always increases
Replies: 6
Views: 5057

### Re: Projectile angle such that distance always increases

Suppose that x(t,\theta) = v_0\cos(\theta)t and y(t,\theta) = -\frac{g}{2}t^2 + v_0\sin(\theta)t , and \theta \in [0,\frac{\pi}{2}] Then, we study the square of the distance : D(t,\theta) = x(t,\theta)^2 + y(t,\theta)^2 = (v_0\cos(\thet...
Tue Aug 30, 2011 4:05 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5915

### Re: Moon or Mars?

Mr_Rose wrote:I'd like to get an orbital delivery system slightly more efficient than a really slow explosion up and running first. Do it right and we can achieve all three in short order....

Skylon... if it works as intented of course
Fri Aug 26, 2011 4:55 am UTC
Forum: General
Topic: The cutest dinosaur?
Replies: 42
Views: 14219

### Re: The cutest dinosaur?

Those are pretty cute dinosaurs :
Thu Aug 25, 2011 5:41 pm UTC
Forum: News & Articles
Topic: Boeing 737 crashes in Resolute Bay, Canada
Replies: 2
Views: 2090

### Re: Boeing 737 crashes in Resolute Bay, Canada

I'm sorry for your friend, psyck0

Two of the persons who died in the crash had survived another airplane crash just three years prior.

They are, at the same time, incredibly lucky and unlucky
Thu Aug 25, 2011 3:19 pm UTC
Forum: Mathematics
Topic: Assignment work - Differentiation
Replies: 5
Views: 1301

### Re: Assignment work - Differentiation

First question : Yes, you did miss something. the derivative of x^x^2 is not 2x^(x^3-x) You need to write x^{x^2} as e^{x^2\ln(x)} but is there a simpler way of finding this? You need to know that tan'(x) = 1+tan²(x), then it's tedious but doable y' = tan(1/x) - 1/x * (1+tan²...
Wed Aug 24, 2011 10:03 am UTC
Forum: Science
Topic: Math/Science Movies
Replies: 11
Views: 2335

### Re: Math/Science Movies

You have also Good Will Hunting
Wed Aug 24, 2011 5:22 am UTC
Forum: Mathematics
Topic: Am I begging the question (and other Analysis questions)
Replies: 12
Views: 2172

### Re: Am I begging the question (and other Analysis questions)

Just a quick remark about a simple but important point. When you say " X_n has a least element, x_n ", you need to justify this. It could appear trivial, but it's not always true: - Not every set has a least element (simple counterexemple : Z) - There are strict orders for which subsets of...
Wed Aug 24, 2011 1:31 am UTC
Forum: School
Replies: 655
Views: 164021

First semester :
- Functionnal analysis
- Algebra
- Stochastic process
- Numerical analysis and simulation

Second semester :
- Distributions and PDE