What Are the Possible Dimensions of V Intersection W in R4?

In summary, the possible dimensions of the subspace V intersection W are 0, 1, and 2. The dimension of the intersection depends on the dimension of the subspaces V and W and the space they are embedded in. It is not possible for subspaces in three-dimensional space to have a 0-dimensional intersection, but a point can exist as an intersection in four-dimensional space. In the given example, the question is asking for the dimension of the kernel of a linear transformation from a 2x3 matrix space to a 4x1 column vector space. The dimension of the intersection can vary depending on the specific linear transformation being used.
  • #1
helix999
32
0
If V and W are 2-dimensional subspaces of R4 , what are the possible dimensions of the subspace V intersection W?

I am new to subspaces, so I have no clue to this question. Help guys!

Options: (A) 1 only (B) 2 only (C) 0 and 1 only (D) 0, 1, and 2 only (E) 0, 1, 2, 3, and 4
 
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  • #2
You don't need to be concerned about the fact that V and W are subspaces, nor that they are embedded in a four-dimensional space.

V and W are two-dimensional, so you know what they look like geometrically, don't you? Now, what are all of the possibilities for the intersection of V and W?
 
  • #3
you mean to say that V and W are 2x2 matrices and their intersection would also be a 2x2 matrix...so the required dimension is 2 only?
 
  • #4
helix999 said:
you mean to say that V and W are 2x2 matrices and their intersection would also be a 2x2 matrix...so the required dimension is 2 only?
No, I didn't say that at all. What does any two-dimensional space look like geometrically?
 
  • #5
Mark44 said:
What does any two-dimensional space look like geometrically?

I am sorry but i am not able to grasp the idea u r trying to put.
 
  • #6
I think the possibility of dimensions would be 0,1, and 2.
 
  • #7
helix999 said:
I am sorry but i am not able to grasp the idea u r trying to put.

Considering the real plane, what is the dimension of a single point? What is the dimension of a line?
 
  • #8
Mark44 said:
Considering the real plane, what is the dimension of a single point? What is the dimension of a line?

it is single dimension
 
  • #9
Mark44 said:
You don't need to be concerned about the fact that V and W are subspaces, nor that they are embedded in a four-dimensional space.

V and W are two-dimensional, so you know what they look like geometrically, don't you? Now, what are all of the possibilities for the intersection of V and W?

You do need to pay some attention to the dimension of the space they are embedded in. If they were embedded in three space a 0 dimensional intersection would be impossible.
 
  • #10
helix999 said:
it is single dimension

I asked two questions. Your answer above is the answer to which question?
 
  • #11
Dick said:
You do need to pay some attention to the dimension of the space they are embedded in. If they were embedded in three space a 0 dimensional intersection would be impossible.

Yes, but I wanted the OP to focus more on the subspaces and not get tangled up in trying to imagine a 4-D space.
 
  • #12
Mark44 said:
I asked two questions. Your answer above is the answer to which question?

point is 0 dimension and line is single dimension
 
  • #13
And a plane has 2 dimensions.
 
  • #14
Mark44 said:
You don't need to be concerned about the fact that V and W are subspaces, nor that they are embedded in a four-dimensional space.

Dick said:
You do need to pay some attention to the dimension of the space they are embedded in. If they were embedded in three space a 0 dimensional intersection would be impossible.

You also need to pay attention to the fact that they are subspaces. The planes (x, y, 0, 0) and (x, y, 0 , 1) have empty intersection. That is impossible for subspaces.
 
  • #15
I got the answer of my question, really appreciate ur posts for making it clear to me. Thnx a bunch!

HallsofIvy said:
You also need to pay attention to the fact that they are subspaces. The planes (x, y, 0, 0) and (x, y, 0 , 1) have empty intersection. That is impossible for subspaces.
why is it impossible for subspaces?
 
  • #16
Dick said:
If they were embedded in three space a 0 dimensional intersection would be impossible.

How come a point can exist as an intersection of subspaces in 4 space but not in 3 space?
 
  • #17
The 2-dimensional subspaces of R4, {(x, y, 0, 0)} and {0, 0, u, v}, have only the single point (0, 0, 0, 0) in common. Two 2- dimensional subspaces in R2 must have a least a 1-dimensional subspace in common.
 
  • #18
helix999 said:
How come a point can exist as an intersection of subspaces in 4 space but not in 3 space?

If the intersection is the single point 0, then if you take union of a basis for one subspace with a basis of the other, the whole set must be linearly independent (otherwise you could construct another intersection point). In the case of two planes, that's 4 linearly independent vectors. Possible in 4 space, not in 3 space.
 
  • #19
those were the new concepts for me...thnx

How do I proceed for such type of questions:

Let V be the real vector space of all real 2 x 3 matrices, and let W be the real vector space of all real 4 x 1
column vectors. If T is a linear transformation from V onto W, what is the dimension of the subspace
{v belongs to V:T(v)=0}?
 
  • #20
helix999 said:
those were the new concepts for me...thnx

How do I proceed for such type of questions:

Let V be the real vector space of all real 2 x 3 matrices, and let W be the real vector space of all real 4 x 1
column vectors. If T is a linear transformation from V onto W, what is the dimension of the subspace
{v belongs to V:T(v)=0}?
In other words, "what is the dimension of the kernel of T" or "what is the nullity of T".
Is that really the entire question? There are many possible answers. For example, T(v)= 0 for all v is a linear transformation and it's kernel is all of V. Since V is a 6 dimensional space (Taking Vij to be the matrix with 1 at "ith row, jth column" and 0 everywhere else, for i= 1 to 2, j= 1 to 3 gives a basis), so that in this example, the dimension of the kernel would be 6.

On the other hand the linear transformation that maps
[tex]\left[\begin{array}{ccc} a & b & c \\d & e & f\end{array}\right]\right)[/tex] to [tex]\left[\begin{array}{c} a \\ 0 \\ 0 \\ 0\end{array}\right][/tex]
has nullity 5: dimension of the kernel is 5.

Perhaps the problem is "what is the smallest possible dimension of the kernel of T".
Since the largest the image of T can be is 4 dimensional, the dimension of "the real vector space of all real 4 x 1 column vectors", the smallest the kernel can be is 6- 4= 2.
 
  • #21
That was the complete question and i guess i understood the explanation.

We solve the integrals like sqrt(1+x^4) dx (limit 0 to 1) by substituting x^2 as tan theta but how do we proceed for integrals like sqrt(1-x^4) dx (limit 0 to 1)?
 
  • #22
helix999 said:
I got the answer of my question, really appreciate ur posts for making it clear to me. Thnx a bunch!


why is it impossible for subspaces?

Any subspace must contain the 0 vector so the intersection of two subspaces must contain at least the 0 vector. It is impossible for the intersection to be empty.
 
  • #23
helix999 said:
That was the complete question and i guess i understood the explanation.

We solve the integrals like sqrt(1+x^4) dx (limit 0 to 1) by substituting x^2 as tan theta but how do we proceed for integrals like sqrt(1-x^4) dx (limit 0 to 1)?
No, we do NOT substitute x^2 as tan theta. If we did then we would have 2 xdx= sec2 theta dtheta- and there is no "x" outside the square root to use with dx.
 
  • #24
then how do we solve such integrals
 
  • #25
HallsofIvy said:
In other words, "what is the dimension of the kernel of T" or "what is the nullity of T".
Is that really the entire question? There are many possible answers. For example, T(v)= 0 for all v is a linear transformation and it's kernel is all of V. Since V is a 6 dimensional space (Taking Vij to be the matrix with 1 at "ith row, jth column" and 0 everywhere else, for i= 1 to 2, j= 1 to 3 gives a basis), so that in this example, the dimension of the kernel would be 6.

On the other hand the linear transformation that maps
[tex]\left[\begin{array}{ccc} a & b & c \\d & e & f\end{array}\right]\right)[/tex] to [tex]\left[\begin{array}{c} a \\ 0 \\ 0 \\ 0\end{array}\right][/tex]
has nullity 5: dimension of the kernel is 5.

Perhaps the problem is "what is the smallest possible dimension of the kernel of T".
Since the largest the image of T can be is 4 dimensional, the dimension of "the real vector space of all real 4 x 1 column vectors", the smallest the kernel can be is 6- 4= 2.

There is only one answer because T is a linear transformation from V onto W.
Therefore the rank of T (or range of T) has to be 4.
Rank(T) + Nullity (T) = dimension of the domain of T (Where V supplies the domain with a dimension of 6).
And then you get Nullity (T) = 2 = dimension of Ker (T) => answer
 

Related to What Are the Possible Dimensions of V Intersection W in R4?

1. What are subspaces?

Subspaces are mathematical objects that are a subset of a larger vector space. They have the same properties as the larger vector space and can be thought of as smaller versions of the larger space.

2. What are the dimensions of subspaces?

The dimension of a subspace is the number of linearly independent vectors that span the subspace. It represents the number of directions or degrees of freedom within the subspace.

3. How do you find the dimension of a subspace?

The dimension of a subspace can be found by determining the number of linearly independent vectors in the subspace. This can be done by using techniques such as Gaussian elimination or finding the null space of a matrix.

4. Can a subspace have a dimension of zero?

Yes, a subspace can have a dimension of zero. This means that the subspace only contains the zero vector and has no other linearly independent vectors. In this case, the subspace is referred to as the trivial subspace.

5. How do dimensions of subspaces relate to linear transformations?

The dimensions of subspaces are closely related to linear transformations. The dimension of the image of a subspace under a linear transformation will be equal to or less than the dimension of the subspace itself. Additionally, the dimension of the null space of a linear transformation will be equal to the difference between the dimension of the domain and the dimension of the image.

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