MHB How Does Archimedes' Estimation of Pi Hold for n=4, 8, 16, 32, ...?

AI Thread Summary
The discussion centers on proving a relationship involving Archimedes' estimation of pi for polygons with edges defined by n = 4, 8, 16, 32, and so on. The equation presented relates the areas of these polygons and involves a geometric interpretation of the terms. A participant initially struggles with the algebra but receives guidance on simplifying the equation and understanding the geometric implications. After some time, the participant successfully solves the problem and expresses intent to share the solution for the benefit of others. The conversation emphasizes the importance of contributing solutions to aid future discussions.
nacho-man
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It has been eons since I've done any trigonometry, but I just can't prove how this following relationship holds for $n = 4, 8, 16, 32, \dots$

The relation is:
$$
2 \biggl( \! \frac{A_{2n}}{n} \! \biggr)^2 = \, 1 - \Biggl( \sqrt{1 - \frac{2A_n^{\phantom{X}}}{n}} \, \Biggr)^{\!2}
$$

I've subbed in points, and it definitely holds.

Using this image as reference, a polygon with $n$ edges and $A_n$ the entire area, we can estimate (albeit very slowly) a unit circle's area.View attachment 4126Any help would be appreciated.
 

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In your equation the right-hand-side takes a square root and then immediately squares the result, what does that amount to? Once you've simplified your equation using that fact, think about what $A_n / n$ and $A_{2n} / n$ represent geometrically, and you can then perhaps reduce the algebra problem to a geometric statement about triangles.
 
Bacterius said:
In your equation the right-hand-side takes a square root and then immediately squares the result, what does that amount to? Once you've simplified your equation using that fact, think about what $A_n / n$ and $A_{2n} / n$ represent geometrically, and you can then perhaps reduce the algebra problem to a geometric statement about triangles.
I have solved this problem now.

Thanks :)
 
nacho said:
I have solved this problem now.

Thanks :)

Great! It's good etiquette to post your solution so that future visitors who come across this thread can also benefit from it :)
 
Bacterius said:
Great! It's good etiquette to post your solution so that future visitors who come across this thread can also benefit from it :)

Yes! definitely.

I will post the solution some time next week, when my work has been assessed (don't want to post a solution with errors and mislead someone :( )
 
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