Draw a Line of Length √3: Tips from an Old Man

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Discussion Overview

The discussion revolves around the challenge of drawing a line of length \(\sqrt{3}\) using a set square. Participants explore various geometric constructions and interpretations of the task, considering both practical and theoretical aspects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • An initial suggestion involves drawing a right triangle with legs of lengths 1 and 2, leading to a hypotenuse of length \(\sqrt{3}\).
  • Another participant proposes constructing a 30-60-90 triangle with a hypotenuse of 2 and one leg of 1, resulting in the other leg being \(\sqrt{3}\).
  • One participant mentions an alternative method using an isosceles right triangle with legs of 1, suggesting that the hypotenuse can be manipulated to yield \(\sqrt{3}\).
  • Concerns are raised about the exactness of the construction, with one participant arguing that the term "exactly" implies that no construction can achieve this with drawing instruments.
  • A later reply discusses the impossibility of providing an exact measure of the line due to its irrational nature, suggesting that such a measure exists only in theoretical mathematics.
  • Humor is introduced with a light-hearted speculation about the identity of the "old man," with a reference to Pythagoras and a nod to the historical figure Hippasus, who is associated with the discovery of irrational numbers.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of constructing a line of length \(\sqrt{3}\) exactly, with some suggesting methods while others argue about the impossibility of achieving exactness with physical drawing tools. No consensus is reached on the validity of the proposed methods.

Contextual Notes

Participants note the limitations of using drawing instruments to achieve exact lengths, particularly with irrational numbers, indicating a dependence on definitions and assumptions about measurement.

Edgardo
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An old man gives you a set square (http://www.buchhandlung-umbach.de/pbs/geodreick.gif ) and then asks you to draw a line of exactly the length [tex]\sqrt{3}[/tex].

How would you do it?
 
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In white: Draw a right triangle of lengths 1 and 2. The hypotenuse will have length [itex]\sqrt{3}[/itex].
 
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first you what units are we using?

second, as far as i can see there are two ways:
first you can straight away construct a 30-60-90 triangle with the hypotenuse (2) and the other leg of 1 (the one which is adjacent to the 60 degree) and then the other leg is sqrt(3).
the second approach is you build an isosceles right triangle with the legs of 1, and then on the hypotenuse you bulid another 1 leg (when the degree between sqrt(2) and the third leg is 90), and then the second hypotenuse is sqrt(3).

this was way too easy, so perhaps i totally misinterpratated your question.
 
@jimmy: Your length would be [tex]\sqrt{5}[/tex]

@ Loop:
I thought about the second approach. You're right.


Next question: What was the name of the old man :biggrin:
 
Edgardo said:
@jimmy: Your length would be [tex]\sqrt{5}[/tex]
Man, talk about a blind spot! I have no explanation for what I was thinking when I wrote that.
 
think quite easy !

1- first you draw a squareroot of 2 by using P=1 AND b =1

then measure the length of the squareroot of 2, take it as p , and take 1 as b, then you can join the end of the these two sides.

correct !

hope so !
 
the word "exactly" means none of these answers are correct, nor is there any correct answer. this is impossible with drawing instruments, but only in the mind, or in the fantasy world of perfect mathematics can this be done exactly.
 
I figure the old man must be Pythagoras.

To get the answer “Exactly” we can’t be drawing so many lines as has been suggested.
Observing the “Square” provided by the old man we see all three sides are neatly inscribe with halfway points. Thus we shall define it as 2 units by 2 units with a H of 2*sqrt{2} units.
After inscribing an exact right angle of 1 by 2, we place a mark on the long length of exactly sqrt{2} by using the midpoint of the H side of the provided square.
Now, again only using the square provided, we see it is long enough to draw a straight line from that marked point to the end of the short line. Giving us an exact sqrt{3} .

But we will never be able to provide an exact measure of that line based on any fractional measure of the units we have selected, ie that measure is irrational.
Note: The old man would appreciate it if you kept this part a secret – he fears the idea that a number can be irrational could cause a public panic! :wink:
 
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