## Search found 2439 matches

Tue Feb 21, 2012 4:11 am UTC
Forum: Mathematics
Topic: Homework: Show that G has a normal subgroup of order nm
Replies: 19
Views: 6591

### Re: Homework: Determine whether a subgroup is normal

OK, then I agree, as long as the "..." conceals 21 lines.

Now write them as the product of disjoint cycles so that you can find out who they really are.
Tue Feb 21, 2012 4:04 am UTC
Forum: Mathematics
Topic: Homework: Show that G has a normal subgroup of order nm
Replies: 19
Views: 6591

### Re: Homework: Determine whether a subgroup is normal

gorcee wrote:So... the conjugates of (1 2)(3 4) would be what?

(1 2) (1 2)(3 4) (1 2)
(1 3) (1 2)(3 4) (1 3)
...
(1 2 3) (1 2)(3 4) (1 2 3)?
Er, I don't agree with that last line. What is the inverse of (1 2 3)?
Tue Feb 21, 2012 3:50 am UTC
Forum: Mathematics
Topic: Homework: Show that G has a normal subgroup of order nm
Replies: 19
Views: 6591

### Re: Homework: Determine whether a subgroup is normal

Well, you don't need any advanced stuff here. A subgroup K of G is normal iff all the conjugates of elements in K are also in K. (This is one of your criteria.) So all you have to do is find out what the conjugates of the elements of K are. The shortcut is that the set of conjugates in S n of any pe...
Tue Feb 21, 2012 3:44 am UTC
Forum: Mathematics
Topic: Homework: Show that G has a normal subgroup of order nm
Replies: 19
Views: 6591

### Re: Homework: Determine whether a subgroup is normal

Sorry; the conjugates (in G) of an element k in G are the elements gkg-1, where g ranges over G.
Tue Feb 21, 2012 3:39 am UTC
Forum: Mathematics
Topic: Homework: Show that G has a normal subgroup of order nm
Replies: 19
Views: 6591

### Re: Homework: Determine whether a subgroup is normal

You can use one of the other criteria.

Hint: What are all the conjugates of (1 2)(3 4)?
Thu Feb 16, 2012 11:27 pm UTC
Forum: Science
Topic: ITT: Baffles baffle Biggles - Chem Eng
Replies: 11
Views: 3010

### Re: ITT: Baffles baffle Biggles - Chem Eng

My intuitive understanding as a non-engineer: Without baffles, all the stuff in your reactor will have a tendency to just go around and around. That seems unlikely to result in rapid homogeneous mixing. For example, once the entire contents of the reactor are rotating with the impeller, your impelle...
Tue Feb 14, 2012 6:11 am UTC
Forum: Gaming
Topic: Magic : The Gathering : The Thread : The Rename
Replies: 1691
Views: 303221

### Re: Magic : The Gathering : The Thread : The Rename

Azrael001 wrote:There seem to be a lot of ways to create an army in the wings, which pop out after a board wipe, I've been playing with that idea a bit. It might make World Slayer and Helvault work together beautifully.
Woooorldslayer!
Fri Feb 10, 2012 9:50 pm UTC
Forum: Mathematics
Topic: Gelca-Andreescu - did I solve this correctly?
Replies: 2
Views: 1011

### Re: Gelca-Andreescu - did I solve this correctly?

Er, you're close.

As I understand the problem, if you have 9 surfaces, A_1 through A_9, you are asked to show that for some i, j, A_i intersect A_j is greater than or equal to 1/9.

There are 9 choose 2 of these intersections, not just 9.
Fri Feb 10, 2012 4:43 am UTC
Forum: Mathematics
Topic: Abstract Algebra, or Topology
Replies: 7
Views: 5927

### Re: Abstract Algebra, or Topology

The boundaries of "algebra" and "topology" are a little too broad to answer the question definitively, but on the whole I would say that topology is more relevant to computer science than algebra, although both are not very relevant (certainly less relevant than analysis). So-cal...
Thu Feb 09, 2012 4:13 pm UTC
Forum: Mathematics
Topic: Bounded infinite shapes
Replies: 3
Views: 1193

### Re: Bounded infinite shapes

No, because of the isoperimetric inequality.
Wed Feb 08, 2012 3:31 am UTC
Forum: Gaming
Topic: Magic : The Gathering : The Thread : The Rename
Replies: 1691
Views: 303221

### Re: Magic : The Gathering : The Thread : The Rename

They're still more prolific than my mate expected - "I looked at putting this in, but I don't have any Locus cards." I suppose if you had four of each of them in a deck that used a lot of colorless mana it'd be alright, but I'd hate to be that starved for color. Cloudpost is actually an a...
Wed Feb 08, 2012 3:17 am UTC
Forum: Mathematics
Topic: Two difficult geometry problems
Replies: 9
Views: 2107

### Re: Two difficult geometry problems

For number 2 (with some trig): For your quadrilateral, if theta is the angle between CD and DA, then cos theta = (CD 2 + DA 2 - AB 2 - BC 2 )/2((AB)(BC) + (CD)(DA)). (You just have to use the law of cosines twice. You also have to use the fact that...
Tue Feb 07, 2012 4:31 pm UTC
Forum: Mathematics
Topic: Hausdorff distance up to isometry? [solved]
Replies: 11
Views: 3714

### Re: Hausdorff distance up to isometry?

An isometry (of a metric space to itself) is a "rigid motion" -- a transformation of the metric space that doesn't change distances. The example you should keep in mind is the rigid motions in Euclidean space (i.e. translations, rotations, and reflections). The point of Hausdorff distance ...
Sun Feb 05, 2012 4:41 pm UTC
Forum: Science
Topic: Common Misconceptions within Physics and Astronomy
Replies: 98
Views: 18333

### Re: Common Misconceptions within Physics and Astronomy

gmalivuk wrote:Yeah, that kinda comes down to how you want to define "color".
Unless the point is that "Ultra Violent" probably isn't a color by any definition.
Sun Feb 05, 2012 3:28 am UTC
Forum: Mathematics
Topic: An Approximation Theory problem
Replies: 1
Views: 776

### Re: An Approximation Theory problem

Well, knowing nothing about approximation theory, here is the approach I instinctively took. The question is basically saying: prove that there is a cylinder containing S of smallest diameter. So we have to think about cylinders. A cylinder can be defined by its diameter, its direction (i.e. the dir...
Fri Feb 03, 2012 5:48 pm UTC
Forum: Gaming
Topic: Magic : The Gathering : The Thread : The Rename
Replies: 1691
Views: 303221

### Re: Magic : The Gathering : The Thread : The Rename

I know I've had my day ruined by Inkmoth Nexus and Kessig Wolf Run on many occasions... I don't think you'd be able to pull that off in a pure-land deck, though... you kinda need dudes in order to last long enough to do it. My deck under the spoiler. It has plenty of dudes, but ironically, the main...
Fri Feb 03, 2012 5:10 pm UTC
Forum: Mathematics
Topic: Help on some estimates...
Replies: 2
Views: 529

### Re: Help on some estimates...

The taylor series for sine is x - x3/6 + x5/120 + ....

I think you forgot the 6.
Thu Feb 02, 2012 2:46 am UTC
Forum: Science
Topic: Can radiometric dating really be used to date the earth?
Replies: 14
Views: 3175

### Re: Can radiometric dating really be used to date the earth?

Regarding 1), this is usually untrue, especially in the case of uranium dating. The oldest things we generally find on Earth are zircon crystals (I think the oldest found is something like 4.2 Gy old), and we use uranium dating to show this. When zircon solidifies from the molten state, it rejects ...
Sat Sep 24, 2011 5:31 am UTC
Forum: Science
Topic: Well, this could change things (neutrinos)
Replies: 289
Views: 45005

### Re: Well, this could change things

They were lower energy. I believe they were on the order of 10 MeV. (EDIT: They ranged from 10 to 40 MeV.) (EDIT 2: The neutrino pulse lasted 13 seconds. If the velocity of the neutrinos depended in any significant way on their energy, surely this range of energies and corresponding velocities would...
Sat Sep 24, 2011 1:24 am UTC
Forum: Science
Topic: Well, this could change things (neutrinos)
Replies: 289
Views: 45005

### Re: Well, this could change things

In this case we have a result that contradicts not only a very well-tested theory, but also the SN1987A "experiment," which despite being completely unplanned, actually has a much more convincing methodology.
Fri Sep 23, 2011 3:45 pm UTC
Forum: Science
Topic: Well, this could change things (neutrinos)
Replies: 289
Views: 45005

### Re: Well, this could change things

OK, I read the paper. I'm not an expert in anything having to do with physics or physics equipment. However, there are an awful lot of things that could go wrong here, because the timing and measurement systems are extremely complex. I understand that they have done a very careful calibration of the...
Fri Sep 23, 2011 4:07 am UTC
Forum: Mathematics
Topic: Should we make students memorize the quadratic formula?
Replies: 61
Views: 8952

### Re: Should we make students memorize the quadratic formula?

I don't think kids should be required to memorize the quadratic formula. However, if you show them the quadratic formula (which you should), then they will memorize it all by themselves. It is the kind of thing that middle- and high-schoolers love more than anything else -- a mechanical formula that...
Fri Sep 23, 2011 4:05 am UTC
Forum: Science
Topic: Well, this could change things (neutrinos)
Replies: 289
Views: 45005

### Re: Well, this could change things

They KNOW they haven't disproved physics.

In SN1987A, a pulse of neutrinos arrived several hours before the light was detected. SN1987A is located 168,000 light years from Earth. If neutrinos travel at 40,001c/40,000, then the neutrinos from SN1987A should have arrived 4 years before they did.
Tue Sep 20, 2011 3:35 am UTC
Forum: Gaming
Topic: Magic : The Gathering : The Thread : The Rename
Replies: 1691
Views: 303221

### Re: magic cards dumped; general magic discussion ensues

12 Island 8 Plains 4 Seachrome Coast 4 Geist of Saint Traft -- 1WU 2/2 hexproof; attack=make tapped+attacking 4/4 flying token, exile token at eoc 4 Sundial of the Infinite 4 Ponder 4 Think Twice -- reprint from TSP 4 Mana Leak 3 Mental Misstep 4 Negate 3 Apostle's Blessing 4 Dismember 4 Snapcaster...
Tue Sep 20, 2011 3:18 am UTC
Forum: School
Topic: How much are you paying for books this semester?
Replies: 59
Views: 29702

### Re: How much are you paying for books this semester?

In college, I never paid more than \$250 for textbooks in a term. I bought them from the campus bookstore. The average was probably about \$150.

But, to be fair, I was always very careful about which books I bought.
Tue Sep 20, 2011 3:08 am UTC
Forum: Mathematics
Topic: Traversal across 3D object
Replies: 9
Views: 1356

### Re: Traversal across 3D object

What exactly is the question?
Tue Aug 30, 2011 1:55 am UTC
Forum: Gaming
Topic: Magic : The Gathering : The Thread : The Rename
Replies: 1691
Views: 303221

### Re: magic cards dumped; general magic discussion ensues

edit 2: MTGO drafting oh god. What are they going to do, just show where all the double-faced cards are? Presumably on MTGO it will just not be possible to see other players' drafted double-faced cards. EDIT: On another topic, I went to my first FNM ever (!) last Friday for my first M12 draft ever ...
Sun Aug 28, 2011 11:32 am UTC
Forum: News & Articles
Topic: Hurricaine Irene: It's pretty big I guess
Replies: 40
Views: 6332

### Re: Hurricaine Irene: It's pretty big I guess

BAD IDEA. Once your house loses power, the freezer and fridge will keep everything inside preserved for a couple days if you do not open the doors. Adding a bowl of water in advance might buy some time (for both), but once the power's out, only open the freezer and fridge to eat everything that's i...
Thu Aug 04, 2011 7:47 am UTC
Topic: Climate Change / Global Warming
Replies: 257
Views: 53766

### Re: Global Warming and Emission Reduction: yea or nay?

I don't think you understood what I was saying. I was saying that pointing out "All of this could be wrong if we have missed something important" is not really relevant. ANYTHING could be wrong if we have missed something important. We have to assume that we didn't miss something important...
Thu Aug 04, 2011 6:39 am UTC
Topic: Climate Change / Global Warming
Replies: 257
Views: 53766

### Re: Global Warming and Emission Reduction: yea or nay?

Keep in mind that not everyone here is a scientist or a mathematician. Obviously global warming is real. There are two categories of objections to the idea: serious objections and stupid objections. Serious objections come from people who aren't convinced by the science because the climate is an ext...
Thu Aug 04, 2011 6:07 am UTC
Forum: News & Articles
Topic: Man sues Hilton over 75¢ newspaper, principle of the thing
Replies: 41
Views: 7221

### Re: Man sues Hilton over 75¢ newspaper, principle of the thi

How can this guy file the lawsuit in federal court? Isn't it going to be dismissed because he should have filed it in a small claims court, or because it's below the \$75,000 threshold for diversity jurisdiction? (I'm not a lawyer.) Alright. Point. That stuff is technically not there by default. But ...
Thu Aug 04, 2011 5:34 am UTC
Forum: Music
Topic: Classical works with the best use of percussion
Replies: 23
Views: 16261

### Re: Classical works with the best use of percussion

Why are you so irate about this? Saying that a particular piece of music is better suited to a science museum than a concert hall is just criticism, even if it is a bit sardonic. If you don't believe there's such a thing as objectively "good" or "bad" music, then understand that ...
Mon Aug 01, 2011 9:19 am UTC
Forum: Science
Topic: Renconciling Apartment Living and Labs
Replies: 10
Views: 1643

### Re: Renconciling Apartment Living and Labs

There are things like this, if you move to the right city.
Mon Aug 01, 2011 9:09 am UTC
Forum: School
Topic: Finding people with similar interests
Replies: 25
Views: 4166

### Re: Finding people with similar interests

OP: You need to talk to someone who has experience helping people with Asperger's. Even here on the fora, you're dealing mostly with neurotypical people who are giving you the advice that worked for them, which is not what you need. People with AS are in a very difficult and alienating position beca...
Mon Aug 01, 2011 5:51 am UTC
Forum: Mathematics
Topic: Help an engineer learn complex analysis
Replies: 8
Views: 1789

### Re: Help an engineer learn complex analysis

Basically, yes, that's what I mean.
Mon Aug 01, 2011 4:03 am UTC
Forum: Mathematics
Topic: Help an engineer learn complex analysis
Replies: 8
Views: 1789

### Re: Help an engineer learn complex analysis

An analytic function is a map on the complex plane that is conformal (i.e. it preserves angles) in most places. (The exceptions are the points where its derivative is zero.) The function e^{\conj{z}} is anti-analytic. It's not analytic because instead of preserving angles, it takes every angle and f...
Fri Jul 29, 2011 6:58 pm UTC
Forum: News & Articles
Topic: GOP Leader Abandons Debt Talks
Replies: 394
Views: 37665

### Re: GOP Leader Abandons Debt Talks

This is bringing out the absolute worst of both parties, but their bad qualities are different. I've never seen the Democrats more spineless, or the Republicans more insane and destructive, than they are today.
Tue Jul 26, 2011 11:10 pm UTC
Forum: Gaming
Topic: Magic : The Gathering : The Thread : The Rename
Replies: 1691
Views: 303221

### Re: magic cards dumped; general magic discussion ensues

Preordain is vastly superior to Ponder in any sane environment. (Vintage is not a sane environment.) The advantage you get from Ponder is that you get to see more cards. This makes it better for combo decks (hence the restriction in Vintage). If you don't care about anything but the very next card y...
Mon Jul 25, 2011 4:00 am UTC
Forum: Mathematics
Topic: Need help with a (silly) argument
Replies: 16
Views: 3021

### Re: Need help with a (silly) argument

Advice: Just walk away.

The argument is nonsense because if you are "dividing by infinity," then the symbol "/" does not have its usual meaning. I can write 1/(Frank Sinatra) = 0, and therefore 1/0 = Frank Sinatra, which makes exactly as much sense as his argument.
Sun Jul 24, 2011 9:02 am UTC
Forum: General
Topic: Hype your ripe snipes 'n' gripes
Replies: 28619
Views: 3535038

### Re: Rant Thread (because we need more ranting)

Here is Amy Winehouse next to the people who were killed in Norway:
* : ********************************************************************************************

This is the ratio of the media coverage:

* : *

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