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#1 Re: Guestbook » Rainbow » 2016-08-20 03:24:16

Notice that the sky is darker above a rainbow than below it. Why? https://www.youtube.com/watch?v=xkDhQGXqwCM.

#2 Jokes » Science Wars » 2016-07-28 22:45:44

Nehushtan
Replies: 3

Physics, Chemistry, Biology, Mathematics – which one is best?

May the mass times acceleration be with you

#5 Re: Puzzles and Games » "Cars Across the Desert Puzzle" » 2016-07-13 14:40:24

wintersolstice wrote:

That was my solution as well.

#7 Re: Guestbook » Rainbow » 2016-07-01 21:25:08

I saw a rainbow yesterday.

62c2984f47035a45d3ba99f92523d707.jpg

#10 Re: Puzzles and Games » Jane’s cryptic crossword clues » 2016-06-04 12:07:28

#32. Duller stuff (6)

#33. Someone for every male child (6)

#12 Re: Help Me ! » GCD of Fibonacci Numbers » 2016-04-23 04:03:35

I would suggest proving that

divides

for all integers m and n. Which means showing that

#13 Re: Exercises » Simple exercises » 2016-04-23 03:58:58

#2. Two circles of radii r and s intersect at two points such that at each point of intersection the tangents to the circles are mutually perpendicular. Show that the centres of the circles and the points of intersection lie on a third circle, and find the radius of this circle.

#14 Exercises » Simple exercises » 2016-04-23 01:10:32

Nehushtan
Replies: 2

I posted this in another thread but here it is for anyone who might wish to have a go.

 
 
 
 

#18 Euler Avenue » The isometry group of the plane » 2016-04-22 14:36:50

Nehushtan
Replies: 0

 
 
 
 

So what possible transformations are isometries of the plane? You might think that there were a whole bunch of them: rotations, reflections, and translations. (A reflection followed by a translation is sometimes called a glide reflection.) In fact the picture is simpler than that: it turns out that reflections and translations can be built up from rotations alone! A translation in a certain direction is simply a reflection in two axes perpendicular that direction, while a rotation about a point O is a reflection in two axes through O.

 
 
 
  Hence any translation is a reflection in two axes perpendicular to the direction of translation whose distance apart is half the distance to be translated.

 
 
 
 

Hence any rotation is a reflection in two axes through the centre of rotation whose angular separation is half the angle to be rotated through.

#19 Re: Help Me ! » sid's new year resolution » 2016-04-21 19:42:42

The number of days he goes for at least one of the activities is

so the number of days he goes for none of them is 366 minus that.

#20 Re: Euler Avenue » Algebraic topology » 2016-04-21 00:18:07

5. HAM-SANDWICH THEOREM

It is always possible to slice a three-layered ham sandwich with a single cut of a knife in such a way that each layer of the sandwich is divided into two exactly equal halves by the cut.

The ham-sandwich theorem can be proved using the Borsuk–Ulam theorem.

#23 Re: Euler Avenue » Algebraic topology » 2016-04-20 11:09:01

4. BORSUK–ULAM THEOREM

 
 
 

 
 
 

#25 Re: Euler Avenue » What had you learned today that you found interesting? » 2016-04-19 09:57:33

Olinguito wrote:

I learn that it is possible to make a tetradecahedron with just regular hexagons and squares.

It is also possible to make a truncated icosahedron with regular pentagons and hexagons.

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