Solving U, V, W Subspaces Problem

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In summary, the conversation discusses a problem involving subspaces U, V, and W and the statement that if U (direct sum) W is equal to V (direct sum) W, then U is equal to V. The participants suggest looking at how this equality affects the vector v in V and considering a counter-example if unable to prove it. They also discuss the importance of understanding the definition of direct sum and its implications for W. Ultimately, the conversation highlights the need for careful thinking and consideration of all relevant factors when attempting to prove or disprove a statement.
  • #1
mivanova
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Hi,
I have thius problem to solve. Please, help me!

1. Prove or disprove if U, V, W are subspaces of V for which
U (dir sum) W = V (dir sum) W then U=V

Thank you in advance!
 
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  • #2
Did you mistype the question? Does it really read V (direct sum) W ?

If it's indeed correct then think carefully about what this implies for any vector v in V and how it may be expressed as a unique sum of vectors v,w from V and W. What does it say about w?

And with this in mind, look at the left-hand side. Is this sufficient alone to conclude U=V?
 
  • #3
Hi,
It's indeed (direct sum) and I think that the statement is it's not true. I can't prove it though.
Thanks!
 
  • #4
If you can't prove it, try looking for a counter-example. Providing a single counter-example without showing why the statement isn't necessarily true would give you full marks, whereas doing the latter only gets you about half marks.
 
  • #5
Oh man, I can't believe I made such a stupid error. Ok, forget what I said earlier and look at V (dir sum) W. What is the subspace spanned by that, taking into account the the definition of direct sum?

What does that say about W? After you're done with this, think about the subspace spanned by U (dir sum) W, and what does it mean for U when the equality stated in the proposition holds.
 

What is the purpose of solving U, V, W subspaces problems?

The purpose of solving U, V, W subspaces problems is to understand the linear relationships between different vectors in a vector space. By solving these problems, we can determine if a set of vectors is linearly independent or dependent, and we can also find a basis for the subspace they span.

What are the key steps in solving U, V, W subspaces problems?

The key steps in solving U, V, W subspaces problems include: identifying the vectors in the subspace, determining if they are linearly independent or dependent, finding the coordinates of each vector in the basis of the subspace, and writing the solution in terms of these coordinates.

How do you determine if a set of vectors is linearly independent or dependent?

A set of vectors is linearly independent if none of the vectors can be written as a linear combination of the others. In other words, no vector in the set is redundant. To determine if a set of vectors is linearly independent or dependent, we can use the method of row reduction or the determinant test.

What is the difference between the basis and the coordinates of a subspace?

The basis of a subspace is a set of linearly independent vectors that span the subspace. The coordinates of a vector in the subspace refer to the coefficients needed to write that vector as a linear combination of the basis vectors. In other words, the coordinates represent the "recipe" for creating the vector using the basis vectors.

How can solving U, V, W subspaces problems be applied in real-life situations?

Solving U, V, W subspaces problems can be applied in a variety of real-life situations, such as in engineering, physics, and computer graphics. It can be used to solve systems of linear equations, analyze the behavior of physical systems, and create 3D models and animations.

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