Is an Equilateral Triangle Possible with Distinct Points in n-Dimensional Space?

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In summary, an equilateral triangle in n-dimensional space is a geometric figure with equal sides that exists in a higher-dimensional space. It is possible to construct an infinite number of equilateral triangles in n-dimensional space with distinct points. This type of triangle differs from a regular triangle in 3-dimensional space in terms of dimension and the number of possible constructions. Studying equilateral triangles in n-dimensional space has various applications in fields such as mathematics, physics, and engineering. However, there are limitations to constructing equilateral triangles in n-dimensional space, such as the availability of distinct points and the applicability in certain higher-dimensional spaces.
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Ackbach
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Here is this week's POTW:

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Let $B$ be a set of more than $2^{n+1}/n$ distinct points with coordinates of the form $(\pm 1,\pm 1,\ldots,\pm 1)$ in $n$-dimensional space with $n\geq 3$. Show that there are three distinct points in $B$ which are the vertices of an equilateral triangle.

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Re: Problem Of The Week # 270 - Jul 03, 2017

This was Problem B-6 in the 2000 William Lowell Putnam Mathematical Competition.

No one answered this week's POTW. The solution, attributed to Kiran Kedlaya and his associates, follows:

For each point $P$ in $B$, let $S_P$ be the set of points with all coordinates equal to $\pm 1$ which differ from $P$ in exactly one coordinate. Since there are more than $2^{n+1}/n$ points in $B$, and each $S_P$ has $n$ elements, the cardinalities of the sets $S_P$ add up to more than $2^{n+1}$, which is to say, more than twice the total number of points. By the pigeonhole principle, there must be a point in three of the sets, say $S_P, S_Q, S_R$. But then any two of $P, Q, R$ differ in exactly two coordinates, so $PQR$ is an equilateral triangle, as desired.
 

FAQ: Is an Equilateral Triangle Possible with Distinct Points in n-Dimensional Space?

What is an equilateral triangle in n-dimensional space?

An equilateral triangle in n-dimensional space is a geometric figure with three sides that are all equal in length and are positioned in n-dimensional space. In other words, it is a triangle that exists in a higher-dimensional space, beyond the familiar three-dimensional space that we experience in our everyday lives.

Is it possible to construct an equilateral triangle in n-dimensional space with distinct points?

Yes, it is possible to construct an equilateral triangle in n-dimensional space with distinct points. In fact, there are infinite possible equilateral triangles that can be formed in n-dimensional space, as long as the points used to construct them are distinct.

How is an equilateral triangle in n-dimensional space different from a regular triangle in 3-dimensional space?

An equilateral triangle in n-dimensional space is different from a regular triangle in 3-dimensional space in that it exists in a higher-dimensional space and has equal sides that are not necessarily constrained to a flat plane. Additionally, the number of possible equilateral triangles in n-dimensional space is infinite, whereas there is only one regular triangle in 3-dimensional space.

What are the applications of studying equilateral triangles in n-dimensional space?

The study of equilateral triangles in n-dimensional space has various applications in mathematics, physics, and engineering. For example, it can be used in the study of higher-dimensional geometry, optimization problems, and computer graphics.

Are there any limitations to constructing equilateral triangles in n-dimensional space?

One limitation to constructing equilateral triangles in n-dimensional space is the availability of distinct points. As the dimension increases, the number of distinct points also increases, making it more challenging to find enough points to construct an equilateral triangle. Additionally, the concept of an equilateral triangle may not be applicable or useful in certain higher-dimensional spaces beyond a certain point.

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