## Search found 213 matches

Wed Oct 09, 2013 4:24 am UTC
Forum: Individual XKCD Comic Threads
Topic: 1275: "int(pi)"
Replies: 95
Views: 28876

### Re: 1275: "int(pi)"

Quicksilver wrote:Pi is exactly 3?

No, int(Pi) is exactly 3. Same for floor(Pi).
This comic gave me a "meh" moment.
Tue Oct 08, 2013 7:01 pm UTC
Forum: What If?
Topic: What-if 0066: "500 MPH"
Replies: 61
Views: 15550

### Re: What-if 0066: "500 MPH"

I need help: could you explain the second to last sentence for me?
"Instead, worry about is the thing that created the 500 mph winds"
Sat Oct 05, 2013 6:59 am UTC
Forum: Mathematics
Topic: Linear functionals in an infinite dimension vector space
Replies: 11
Views: 3017

### Re: Linear functionals in an infinite dimension vector space

lalop wrote:I wonder what are the potential pitfalls in well-ordering the index set and labeling them 1,2,...,w,..

Well, if the index set is uncountable you wouldn't be able to lable them all iirc.
Tue Sep 24, 2013 11:22 am UTC
Forum: Individual XKCD Comic Threads
Topic: 1268: "Alternate Universe"
Replies: 200
Views: 33549

### Re: 1268: "Alternate Universe"

I sometimes find myself in a universe where people use sporks, or even worse - small sporks(the size of teaspoons).
Sun Sep 22, 2013 4:58 pm UTC
Forum: Mathematics
Topic: Is there any way to take the square root of a matrix?
Replies: 18
Views: 3882

### Re: Is there any way to take the square root of a matrix?

Wed Sep 18, 2013 4:15 am UTC
Forum: Individual XKCD Comic Threads
Topic: 1266: "Halting Problem"
Replies: 83
Views: 20994

### 1266: "Halting Problem"

Title text: "I found a counterexample to the claim that all things must someday die, but I don't know how to show it to anyone."

Thu Sep 05, 2013 9:00 pm UTC
Forum: Mathematics
Topic: n(v) = n(v+1)*d+n(v-1)*u, v:[0,a+b] find n(v) given u,d,a,b
Replies: 4
Views: 1241

### Re: n(v) = n(v+1)*d+n(v-1)*u, v:[0,a+b] find n(v) given u,d,

Do you mean Phi and Psi? Those are greek letters, usually used to signify the golden ratio and -1/(golden ratio). The golden ratio is the positive solution to x 2 =x+1. Multiply both sides by x n and you get x (2+n) =x (n+1) +x n , which is quite the same relation as the one the fibo...
Thu Sep 05, 2013 5:24 pm UTC
Forum: Mathematics
Topic: n(v) = n(v+1)*d+n(v-1)*u, v:[0,a+b] find n(v) given u,d,a,b
Replies: 4
Views: 1241

### Re: n(v) = n(v+1)*d+n(v-1)*u, v:[0,a+b] find n(v) given u,d,

I'd go with it like the Fibonacci sequence. n v = u*n v-1 +d*n v+1 => n v+1 =(1/d)*n v -(u/d)*n v-1 substitute k=1/d, l=-u/d, k+l=-1 d+u=1 => u/d-1/d=1 => k+l=-1 n v+1 =k*n v +l*n v-1 From there I'd follow the derivation here , but instead of using x^2=x+1 , I'd use x^2=k*x+l , knowing that k+l = -1...
Fri Aug 30, 2013 6:53 am UTC
Forum: Individual XKCD Comic Threads
Topic: 1258: First
Replies: 72
Views: 22224

### Re: 1258: First

Fifteenth!

Thank you, Mr. Munroe.
Thu Aug 08, 2013 10:31 am UTC
Forum: Logic Puzzles
Topic: A board game based on ´symmetry´
Replies: 15
Views: 9019

### Re: A board game based on ´symmetry´

I want it in board form... Oh wait, I can buy reversie and play it with that.
This game feels like a mix of reversie with go.
Wed Aug 07, 2013 8:18 am UTC
Forum: Individual XKCD Comic Threads
Topic: 1248: "Sphere"
Replies: 78
Views: 18487

### Re: 1248: "Sphere"

Am I the only one raging about the fact that the Earth is not a sphere or an oblate spheroid. Randall, please refer to this.
Tue Aug 06, 2013 11:22 am UTC
Forum: What If?
Topic: What-If 0057: "Dropping a Mountain"
Replies: 61
Views: 19870

### Re: What-If 0057: "Dropping a Mountain"

BlackHatGuy was right, you didn't drop it from high enough, earth's escape velocity is 11.186 km/s, and at the best height you dropped it you only reached 10 km/s You could've gone higher, tho it would have diminishing effects. Earth can pull stuff everywhere, although the sun would probably win thi...
Mon Aug 05, 2013 1:35 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1247: "The Mother of All Suspicious Files"
Replies: 70
Views: 33358

### Re: 1247: "The Mother of All Suspicious Files"

RAR and ZIP? I think randall is going crazy.
Sun Jul 28, 2013 6:55 pm UTC
Forum: Mathematics
Topic: Trying to find a way to describe this "set" of numbers
Replies: 24
Views: 7220

### Re: Trying to find a way to describe this "set" of numbers

Equality is more fundamental than arithmetic, its necessary for sets, and the elements of sets, to make sense. In particular, in you numbers you talk about "2". Well, if, when I write "2", I always mean the same thing, then... it doesn't really make sense to say that "2=2&q...
Fri Jun 28, 2013 5:39 pm UTC
Forum: Logic Puzzles
Topic: Test-solve my puzzles, please
Replies: 174
Views: 59167

### Re: Test-solve my puzzles, please

Snark wrote:
Spoiler:
How is there a 4? There must be at least one visible skyscraper of height 5 or 6 in each row and column, right? Which makes the minimum sum 5, right? I'm missing something big here.

Spoiler:
You could have a 6/5, which is less than 4.
Sun Jun 16, 2013 7:06 pm UTC
Forum: Logic Puzzles
Topic: Test-solve my puzzles, please
Replies: 174
Views: 59167

### Re: Test-solve my puzzles, please

I managed to solve it, but I needed to assume 2 things and go from there and then I've seen there are no contradictions. I also assumed the solution is unique, is it? I'm not sure if I'm reading correctly, but are there are 9 spaces between the stars in the 8 column? Ha, you are, for some reason I ...
Sun Jun 16, 2013 6:09 pm UTC
Forum: Logic Puzzles
Topic: Test-solve my puzzles, please
Replies: 174
Views: 59167

### Re: Test-solve my puzzles, please

I managed to solve it, but I needed to assume 2 things and go from there and then I've seen there are no contradictions. I also assumed the solution is unique, is it? I counted wrong, it's 11x11, not 10x10, so my solution is wrong. back to work. A small dot is no star, a large dot is a star: ht...
Sun Jun 16, 2013 11:15 am UTC
Forum: Mathematics
Topic: Neat Mental Arithmetic Tricks
Replies: 33
Views: 5566

### Re: Neat Mental Arithmetic trickses

91 is the first number that looks prime but isn't, and the only one under 100. "Instant" prime detector for numbers under 100: Is it 91? Not prime! Check divisibility by 2, 3 and 5 (this should be nearly instant -- is it even? Does it end in 5? Add up digits, do they sum to a number divis...
Sun Jun 16, 2013 11:07 am UTC
Forum: Mathematics
Topic: Validity of deductive arguments involving "if" and "then"
Replies: 11
Views: 1763

### Re: Validity of deductive arguments involving "if" and "then

thanks! :wink: When P is true, it's obvious: "If it's raining, John has an umbrella" is true when it's raining and John has an umbrella, and it's false when it's raining but John has no umbrella. Simple questions derive from the above. Do you establishing what you said on a linguistic/gra...
Tue May 21, 2013 6:12 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1214: "Geoguessr"
Replies: 102
Views: 33677

### Re: 1214: "Geoguessr"

Actually, the best guess I had was where it said the difference was 0.000 km, so, under a meter off. Only got ~6000-7000 points from that.
Then today I did something with a difference of 0.012 km, and got the same amount of points. Dammit diminishing returns.
Mon May 20, 2013 6:56 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1214: "Geoguessr"
Replies: 102
Views: 33677

### Re: 1214: "Geoguessr"

Best feature in this game: the compass at the top left.
I wonder why it always puts me in russia, spain, mexico, the USA/alaska, and australia/england(which are easy due to left-side-of-the-road). There are other places in the world! I think.
Mon May 13, 2013 4:17 am UTC
Forum: Logic Puzzles
Topic: What is s?
Replies: 3
Views: 3100

### Re: What is s?

snowyowl wrote:Can't I just compile and run the code to see what it does?

Probably, but you'd need to add some code to define s and later on print in some way.
Sun May 12, 2013 10:05 am UTC
Forum: Logic Puzzles
Topic: What is s?
Replies: 3
Views: 3100

### Re: What is s?

Spoiler:
s>>=1 shifts the bits of s one spot to the right. After it does that, if the shifted s isn't 0, j is incremented. The output will be log2(input), rounded down. Thus, for the inputs (1,2,4,8), the outputs will be (0,1,2,3) respectively.
Sun Apr 21, 2013 12:56 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1201: "Integration by parts"
Replies: 81
Views: 25867

### Re: 1201: "Integration by parts"

Matching up coefficients gives: a2 = 1 a1 + 2 a2 = 0 a0 + a1 = 0 This is a linear system, three equations in three unknowns. The unique solution is: a2 = 1 a1 = -1/2 a0 = 1/2 That is: ∫ e^x x^2 dx = e^x (x^2 - 1/2 x + 1/2) + C, of course. Actually, the unique solution to that system of equations is...
Sat Apr 06, 2013 11:18 am UTC
Forum: Individual XKCD Comic Threads
Topic: 1190: "Time"
Replies: 107346
Views: 51696994

### Re: 1190: "Time"

We've got an amazing 0.3% of the forum's posts right here, all for The One Comic.

What's she looking at?
Sat Apr 06, 2013 11:10 am UTC
Forum: Mathematics
Topic: Probabilities with Ω={}
Replies: 12
Views: 2608

### Re: Probabilities with Ω={}

Xenomortis wrote:Except the OP already has P({}) = 0 as an axiom.
You have a problem right from the start with the implication 0 = 1. You don't want to do any work after that.

True.
Sat Apr 06, 2013 7:53 am UTC
Forum: Mathematics
Topic: Probabilities with Ω={}
Replies: 12
Views: 2608

### Re: Probabilities with Ω={}

If X is the empty set, then X and X are disjoint (just try and look for an element in the intersection...), and so the probability P(X or X) = P(X) + P(X) = 1 + 1 = 2. But X or X is X, since... it's the empty set. So we get 1 = 2. I don't see a way to make sense of the probability with an empty eve...
Fri Apr 05, 2013 5:23 am UTC
Forum: Individual XKCD Comic Threads
Topic: 1195: "Flowchart"
Replies: 60
Views: 11302

### Re: 1195: "Flowchart"

Reminds me of that episode of The Big Bang Theory in which Sheldon tries to be friends with that guy to get access to the good computers.
One should not mess with flow charts.
Wed Apr 03, 2013 3:31 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1190: "Time"
Replies: 107346
Views: 51696994

### Re: 1190: "Time"

Interesting infographic: Shows number of forum posts for each TimeFrame/Newpix. The timeframes are scaled to outsider time so that they are doubly spaced after 242 when they started updating hourly. http://kieryn.com/xkcd-time/img/forum_activity.png Is that data represantation in logarithmic scale ...
Wed Apr 03, 2013 3:21 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1190: "Time"
Replies: 107346
Views: 51696994

### Re: 1190: "Time"

Interesting infographic: Shows number of forum posts for each TimeFrame/Newpix. The timeframes are scaled to outsider time so that they are doubly spaced after 242 when they started updating hourly. http://kieryn.com/xkcd-time/img/forum_activity.png Is that data represantation in logarithmic scale ?
Tue Apr 02, 2013 5:38 pm UTC
Forum: Mathematics
Topic: Simple (probably) triangle problem (need help)
Replies: 20
Views: 3449

### Re: Simple (probably) triangle problem (need help)

You could, instead of stage 2 in my post, find the parameterization of the line through p1,using the (signed-)distance as parameter: (x1+d*cos(a2),y1+d*sin(a2)) and insert it into the equation at stage 1 to obtain the distance that way(solve for the d). Edit: This is just like what the one above me ...
Tue Apr 02, 2013 5:28 pm UTC
Forum: Mathematics
Topic: Simple (probably) triangle problem (need help)
Replies: 20
Views: 3449

### Re: Simple (probably) triangle problem (need help)

It's probably not homework, but I'll put it in a spoiler. If it is homework, don't go far with the angles and lengths, think how you can get the coordinates of the intersection with the known data. Assuming p1(x1,y1),p2(x2,y2),p3(x3,y3) 1. Get the equation of the line p2,p3: ...
Thu Mar 28, 2013 11:26 am UTC
Forum: Individual XKCD Comic Threads
Topic: 1190: "Time"
Replies: 107346
Views: 51696994

### Re: 1190: "Time"

Am I the only one who was thinking it will end with Neil Patrick Harris' face and a text bubble saying '-dary! True story.'?
Wed Mar 27, 2013 3:49 pm UTC
Forum: Logic Puzzles
Topic: Pennies in Boxes
Replies: 86
Views: 52447

### Re: Pennies in Boxes

Adding to the above: According to the US mint site , 1 cent weighs 2.5 gram. The boxes contain 125,000,000 pennies, that's 312,500,000 gram in copper plated zinc, or 312,500 kilogram, for those of you using the imperial system, ~688,937.5 pounds. I have no idea how the hell that cardboard box was br...
Tue Mar 26, 2013 11:50 am UTC
Forum: Mathematics
Topic: Name this curve
Replies: 23
Views: 5120

### Re: Name this curve

I've made it in geogebra with varying length. I can't upload the file here, if anyone wants I'll upload it to dropbox or something. I exported a gif of the distance going from 0 to 3, and it looks neat: https://dl.dropbox.com/u/17511637/awsome.gif a=|AE 1 |=|AE 2 | Translating the circle such that t...
Thu Feb 21, 2013 8:00 pm UTC
Forum: Logic Puzzles
Topic: Tea or Coffee
Replies: 13
Views: 6266

### Re: Tea or Coffee

Correct idea, though numbers are slightly off. After the first mixture, given that teacup now has 110ml total volume, the second extraction would yield 9 1 / 11 ml tea and 10 / 11 ml coffee, not "9 mL tea and 1 mL Coffee" as stated . So after the second mixture, both vessels would contain...
Wed Feb 06, 2013 12:39 pm UTC
Forum: Language/Linguistics
Topic: You keep using that word...
Replies: 39
Views: 13689

### Re: You keep using that word...

The word "stupid".
Tue Jan 22, 2013 10:18 am UTC
Forum: What If?
Topic: What-If 0029: "Spent Fuel Pool"
Replies: 167
Views: 46684

### What-If 0029: "Spent Fuel Pool"

http://what-if.xkcd.com/29/ What if I took a swim in a typical spent nuclear fuel pool? Would I need to dive to actually experience a fatal amount of radiation? How long could I stay safely at the surface? —Jonathan Bastien-Filiatrault I waited and I waited, and no thread, so I decided to man up and...
Thu Jan 17, 2013 3:27 pm UTC
Forum: Mathematics
Topic: Sum of first m terms of a combinatorial number
Replies: 3
Views: 977

### Re: Sum of first m terms of a combinatorial number

tomtom2357 wrote:2 choose 3=0, because you can't choose 3 items from 2 items.

Note that (7 choose 5)+(6 choose 4)=36, the other terms are all 0.
Tue Jan 15, 2013 10:05 am UTC
Forum: Logic Puzzles
Topic: Solve ALL of the Mazes [solutions]
Replies: 29
Views: 9051

### Re: Solve ALL of the Mazes [solutions]

Here's a new and improved difficult maze sequence: 1: ####### 2: ####### 3: ####### #s##### #s#...# #s..### #.#...# #.#.#.# #.#.### #.#.#.# #.#.#.# #.#.### #.#.#.# #.#.#.# #.#...# #.#.#r# #.#.#r# #.#t#.# #.#.### #.#.### #.###.# #....e# #....e# #..r#e# ####### ####### ####### Moving maze 1 from &quo...

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