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Cylinder placing...

Cylinder placing...

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r
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Suppose you wish to place 7 equally-sized cylinders of length l and diameter d in such a way that they all touch each other. What is the largest value of l/d such that this is impossible?

richjohnson
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Originally posted by royalchicken
Suppose you wish to place 7 equally-sized cylinders of length l and diameter d in such a way that they all touch each other. What is the largest value of l/d such that this is impossible?
Do you mean that they all touch at least one other cylinder? or that they each touch every other cylinder?

r
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Each touches every other. I haven't even tried this puzzle yet, and I don't know the answer, but I think I'll give it a go.

r
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I've solved it. Anyone else? Ideas...?

ct[

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20

r
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Erm...no. How did you arrive at that?

bbarr
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Originally posted by royalchicken
Erm...no. How did you arrive at that?
Perhaps Fregean 'flash-grasping' of necessary truths?

r
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Actually, ingenuity and trigonometry suffice. Are you guys going to give it a go, or wait around for Acolyte 😉?

bbarr
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Originally posted by royalchicken
Actually, ingenuity and trigonometry suffice. Are you guys going to give it a go, or wait around for Acolyte 😉?
Not me, the only interest I have in mathematics consists in its reduction to first-order logic with identity and set-theory. I'm a foundational type of guy.😀

r
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Ah. Pity. You'd be good at it. My chief interest in mathematics is currently analytic number theory. They don't teach THAT in school 😉.

r
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No takers? Acolyte?

Acolyte
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Originally posted by royalchicken
No takers? Acolyte?
Erm... I don't have the dexterity to construct a physical model with biros, and I can't really picture how the 7 cylinders are arranged, much less prove that they have to be arranged in a particular way. 😕

r
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A wee hintie: 7 cylinders is the largest number for which this can be done (easy to prove), and there is only one configuration (consider that as fact; it is). To visualize it, use unsharpened pencils, or cigarettes, or just draw them (that's what I did-probably the easiest). Figure out 3, then 4, etc. Then look at limiting positions.

What is a biro?

MT

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Originally posted by royalchicken
A wee hintie: 7 cylinders is the largest number for which this can be done (easy to prove), and there is only one configuration (consider that as fact; it is). To visualize it, use unsharpened pencils, or cigarettes, or just draw them (that's what I did-probably the easiest). Figure out 3, then 4, etc. Then look at limiting positions.

What is a biro?
A biro is a very cheap pen, a ballpoint oen

r
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can't u just fit them into a hexagon and let them be any size?

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