Need some help on this problem:

Prove that if V is finite dimensional and U1....Um are subspaces of V, then

dim(U1+...+Um) is less than or equal to dim U1+...+Um.

Thanks

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- February 4th 2007, 05:12 PMtaypezLinear Algebra II
Need some help on this problem:

Prove that if V is finite dimensional and U1....Um are subspaces of V, then

dim(U1+...+Um) is less than or equal to dim U1+...+Um.

Thanks - February 4th 2007, 05:44 PMThePerfectHacker
Again, I will assume that means the direct sum of vector spaces, as in the Cartesian product.

For simplicity sake, I will work with only two vector spaces. . And the more general case will follow easily and similarly.

I did not confirm this because of laziness, but I believe that if is a basis for , and is a basis for . Then, is**not necessarily**a basis for but**it is**a spanning set of vectors. And hence, since the size of the basis is less than the size of the spanning set we have,

Because is the size of spanning set and is the size (cardinality) of the dimension (basis) of those spanning vectors.