True or false and why?
(a) There exists a vector space consisting of exactly 100 vectors.
(b) There exists a vector space of dimension 100.
(c) In a vector space of dimension 3, any three vectors are linearly independent.
(d) In a vector space of dimension 3, any four vectors are linearly dependent.
(e) Any vector space of dimension 2 has exactly two subspaces.
(f) Any vector space of dimension 2 has in?nitely many subspaces.
(g) Any vector space of dimension 3 can be expanded by four vectors.
(h) Any vector space of dimension 3 can be expanded by two vectors.
(i) Three vectors are linearly dependent if and only if one of them can be written as a linear combination of the other two.
(j) The column space and row space of the same matrix A will have the same dimension.

Respuesta :

Answer and explanation:

(a) There exists a vector space consisting of exactly 100 vectors.

False. All vector space consists of an infinite number of vectors.

(b) There exists a vector space of dimension 100.

True. There exist vector spaces of N dimensions. You can peak an N integer you desire (in this case N=100)

(c) In a vector space of dimension 3, any three vectors are linearly independent.

False. Thre different vectors could be linearly dependent. Example: (1,1,0),(1,1,1),(0,0,1). The first and the third vector form the second one.

(d) In a vector space of dimension 3, any four vectors are linearly dependent.

True. The maximum number of linearly independent vectors in a vector space of dimension 3 is 3. Therefore any additional vector will be linearly dependent with the others.

(e) Any vector space of dimension 2 has exactly two subspaces.

False. Any vector space has an infinite number of subspaces, independently of its dimension.

(f) Any vector space of dimension 2 has infinitely many subspaces.

True. I explained this in the previous statement.

(g) Any vector space of dimension 3 can be expanded by four-vectors.

False. You expand subspaces of dimension n by adding m linearly dependent vectors to complete the space of dimension (n+m) in which exist. You don´t expand vector spaces.

(h) Any vector space of dimension 3 can be expanded by two vectors.

False. I explained this in the previous statement.

(i) Three vectors are linearly dependent if and only if one of them can be written as a linear combination of the other two.

False. One of the three vectors could be linearly dependent with one of the other 2 two vectors and linearly independent with the other.

(j) The column space and row space of the same matrix A will have the same dimension.

True. The rank of any matrix is the dimension of the columns or the rows. Been only a single number, columns space and row space have to have the same dimension. This can be explained with the rank-nullity theorem.

Based on the questions asked about the vectors, the correct options will be:

(a) False. This is because all linear combinations of the basis vectors have to be in the vector space.

  • (b). True. This is because R100 is a vector space of dimension 100.

  • (c ). False. This is because vectors (1,0,0)T,(2,0,0)T and (3,0,0)T in R3 are linearly dependent.

(d). True. This is because in a vector space of dimension 3, a maximum of 3 vectors only can be linearly independent.

(e).False. Span{(1,0)T}, span {(0,1)T}, and span { (1,0)T,(0,1)T} are all subspaces of R2. Every vector space is a subspace of itself.

(f).True.

(g) False. A maximum of 3 vectors only can be linearly independent in a vector space V of dimension 3. All linear combinations of the basis vectors will be in the vector space. It cannot be expanded by 4 vectors.

(h) False. For the same reason as in (g) above.

(i).True. This is simply the definition of linear dependence.

(j).True. The dimension of Row(A) or Col(A) for any matrix A is called the rank of A.

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