# Thread: The intersection of three-dimensional hyperplanes

1. ## The intersection of three-dimensional hyperplanes

Dear mathematicians

I have a question regarding the intersection of three dimensional hyperplanes in R^4. I know that the intersection of two planes in R^2 is a line. So the intersection of a finite number of planes is a line and we can thought of the planes as a pages of an open book.

How can we define the intersection of three-dim hyperplanes in R^4. Is it true that the intersection of finite number of hyperplanes is a common plane between them, if so how can we visualise and sketch this.

2. ## Re: The intersection of three-dimensional hyperplanes

Hey student2011.

You need to setup a matrix system (Ax=b) corresponding to the hyper-planes and then look at the rank of the solution. That will tell whether it even has a solution and if so whether its a point/line/plane/etc.

3. ## Re: The intersection of three-dimensional hyperplanes

Thank you so much chiro, so the intersection of finite number of hyperplanes in R^4 is not necessarily a plane.

4. ## Re: The intersection of three-dimensional hyperplanes

Dear assistants

I have another question:

Is it true that " there is n 3-dim hyperlanes in R^4 such that the intersection between them is a plane, for all positive integer n"

5. ## Re: The intersection of three-dimensional hyperplanes

Originally Posted by student2011
Dear mathematicians

I have a question regarding the intersection of three dimensional hyperplanes in R^4. I know that the intersection of two planes in R^2 is a line.
Did you mean "two planes in R^3"? There cannot be two distinct planes in R^2.
Even assuming you mean R^3, this, itself, is not generally true. The intersection of two planes in R^2 is (1) a line or (2) the empty set or (3) a plane.

So the intersection of a finite number of planes is a line and we can thought of the planes as a pages of an open book.

How can we define the intersection of three-dim hyperplanes in R^4. Is it true that the intersection of finite number of hyperplanes is a common plane between them, if so how can we visualise and sketch this.