Can you imagine that? (I)

Geometry Level 4

How may different orthants are there in R 10 \mathbb R^{10} ?

Clarification : An orthant the analogue in n n -dimensional Euclidean space of a quadrant in the plane or an octant in three dimensions.


The answer is 1024.

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3 solutions

Zeeshan Ali
Jan 14, 2016

In R 2 \mathbb R^{2} , there are 2 2 = 4 2^2=4 different quadrants .

In R 3 \mathbb R^{3} , there are 2 3 = 8 2^3=8 different octants .

In R 4 \mathbb R^{4} , there are 2 4 = 16 2^4=16 different orthants.

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In R 10 \mathbb R^{10} , there are 2 10 = 1024 \boxed{2^{10}=1024} different orthants.

Generalization:

Let R n \mathbb R^{n} be the n d i m e n s i o n a l n-dimensional space. Then there are 2 n 2^n different orthants .

I guess you can't really call them "quadrants" then ;) In 3-D they are called octants

Otto Bretscher - 5 years, 5 months ago

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Thank you sir..! Is there any general name for quadrant or octant or so, please?

Zeeshan Ali - 5 years, 5 months ago

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Yes the general term is orthant or hyperoctant . Most mathematicians prefer hyperoctant, I suppose, since the usage of "hyper-" in this context follows a pattern of taking a 3-D term and generalizing it to n-space, as in hyperplane or hypersphere.

Otto Bretscher - 5 years, 5 months ago

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@Otto Bretscher Thanks again..! I have edited the question..

Zeeshan Ali - 5 years, 5 months ago

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@Zeeshan Ali I was not really serious about my remark. It just sounds funny to have 1024 quadrants of something ;)

Otto Bretscher - 5 years, 5 months ago

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@Otto Bretscher Well... of course ..!

Zeeshan Ali - 5 years, 5 months ago

@Otto Bretscher It is all about "Fun..!" on brilliant.org :)

Zeeshan Ali - 5 years, 5 months ago

In accordance to Bosonic string theory, there exist 26 26 dimensions of space time. Does it conclude that there exist 2 26 2^{26} orthants in space time?

@Michael Mendrin @Otto Bretscher

Swapnil Das - 5 years, 5 months ago

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Well... I think .. Yes! :)

Zeeshan Ali - 5 years, 5 months ago

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@Zeeshan Ali I am in doubt because of considering time as a dimension.

Swapnil Das - 5 years, 5 months ago

No! We are talking about a 26 dimensional manifold here, not 26 dimensional Euclidean space. In the context of a manifold, the notion of orthants does not make sense. (Does a torus have four quadrants?)

Otto Bretscher - 5 years, 5 months ago

Aren't the 26 dimension actually not of space-time? Meaning that there are 3 dimensions of space, and one temporal dimension (in terms of the math). So the rest of the 22 are more so hyperspace I think...

Ali Hyder - 5 years, 4 months ago

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@Ali Hyder Oh, yes! Silly misconception.

Swapnil Das - 5 years, 4 months ago
Adrian Castro
Jan 17, 2016

You can distill the solution down to the basics. We know that a quadrant, octant, etc... Can be defined as a permutation of the values +or - assigned to the number of dimensions n in R n . \mathbb{R}^n. Therefore, there exist 2 n 2^n orthants in R n . \mathbb{R}^n.

Agil Saelan
Jan 17, 2016

I think you should change the link to wikipedia because the answer is there

Well... right ! Thank you very much ..

Zeeshan Ali - 5 years, 5 months ago

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