# Will there always be a vector product for 2 vectors in a 3d plane?

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• KittiesAre_Cute
KittiesAre_Cute
TL;DR Summary
Will there always be a cross product for 2 vectors when they have components in all 3 plane. I mean if they are in xy plane we just take the vector product to be the z axis, but when they have components in all 3 dimensions, will there always be a 2d plane that contains both of them (not the x,y or z plane) so we can take the perpendicular
Hi, it is my first post here so please dont mind any mistakes if you see them. I am currently learning vectors and one thing that I do not understand is if there will always be a vector product for 2 vectors when they have components in all 3 plane. I mean if they are in xy plane we just take the vector product to be the z axis, but when they have components in all 3 dimensions, will there always be a 2d plane that contains both of them (although not the x,y or z plane) so we can take the perpendicular to that plane and get the vector product.

weirdoguy said:
Yes.
So youre saying 2 vectors in a 3d plane will always have be contained in a common 2d plane?

Any two (linearly independent) vectors span a two-dimensional subspace. If they are linearly independent the cross product is zero.

Orodruin said:
Any two (linearly independent) vectors span a two-dimensional subspace. If they are linearly independent the cross product is zero.
Is there a specific reason or proof for that? (Asking so that I can search and learn more)

KittiesAre_Cute said:
So youre saying 2 vectors in a 3d plane will always have be contained in a common 2d plane?
Just rotate your coordinate system so that the x axis is parallel to one vector, then rotate it around that vector until the other one lies in the x-y plane.

KittiesAre_Cute said:
So youre saying 2 vectors in a 3d plane will always have be contained in a common 2d plane?
At least in one common plane. If the vectors are co-linear or one is a zero-vector, they are contained in infinitely many common planes. Otherwise they span a triangle, which defines a unique plane.

KittiesAre_Cute said:
Is there a specific reason or proof for that? (Asking so that I can search and learn more)
The cross product is a Lie multiplication of a three-dimensional simple real Lie algebra. From here on there are paths in many directions to learn more. Simply start to understand my wording.

If you are more interested in the geometrical part of your question, then look at Geometric Algebra by Eric Chisolm.

If you are especially interested in the cross-product in physics, then search for "right-hand-rule" or "Fleming's rule", e.g. https://www.khanacademy.org/test-pr...es/magnetism-mcat/a/using-the-right-hand-rule

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