- Let be vectors in ℝ
^{n}. The parallelepiped determined by these vectorsis defined as

Now let A be an n × n matrix. Show that

is also a parallelepiped.

- In the context of Problem 1, draw Pwhere e
_{1},e_{2}are the standard basis vectors for ℝ^{2}. Thus e_{1}=,e_{2}=. Now supposewhere E is the elementary matrix which takes the third row and adds to the first. Draw

In other words, draw the result of doing E to the vectors in P

. Next draw the results of doing the other elementary matrices to P. An elementary matrix is one which is obtained from doing one of the row operations to the identity matrix. - Determine which matrices are in row reduced echelon form.
(a)

(b)(c) - Row reduce the following matrices to obtain the row reduced echelon form. List the pivot columns in
the original matrix.
(a)

(b)(c) - Find the rank of the following matrices. If the rank is r, identify r columns in the original matrix
which have the property that every other column may be written as a linear combination of these.
Also find a basis for column space of the matrices.
(a)

(b)(c)(d)(e) - Suppose A is an m × n matrix. Explain why the rank of A is always no larger than min.
- A matrix A is called a projection if A
^{2}= A. Here is a matrix.Show that this is a projection. Show that a vector in the column space of a projection matrix is left unchanged by multiplication by A.

- Let H denote span. Find the dimension of H and determine a basis.
- Let H denote span. Find the dimension of H and determine a basis.
- Let H denote span. Find the dimension of H and determine a basis.
- Let M = . Is M a subspace? Explain.
- Let M = . Is M a subspace? Explain.
- Let w ∈ ℝ
^{4}and let M =. Is M a subspace? Explain. - Let M = . Is M a subspace? Explain.
- Let w,w
_{1}be given vectors in ℝ^{4}and defineIs M a subspace? Explain.

- Let M = . Is M a subspace? Explain.
- Let M = . Is M a subspace? Explain.
- Suppose is a set of vectors from F
^{n}. Show that spancontains 0. - Prove the following theorem: If A,B are n×n matrices and if AB = I, then BA = I and B = A
^{−1}. Hint: First note that if AB = I, then it must be the case that A is onto. Explain why this requires span= F^{n}. Now explain why, this requires A to be one to one. Next explain why A= 0 and why the fact that A is one to one implies BA = I. - Here are three vectors. Determine whether they are linearly independent or linearly dependent.
- Here are three vectors. Determine whether they are linearly independent or linearly dependent.
- Here are three vectors. Determine whether they are linearly independent or linearly dependent.
- Here are four vectors. Determine whether they span ℝ
^{3}. Are these vectors linearly independent? - Here are four vectors. Determine whether they span ℝ
^{3}. Are these vectors linearly independent? - Determine whether the following vectors are a basis for ℝ
^{3}. If they are, explain why they are and if they are not, give a reason and tell whether they span ℝ^{3}. - Determine whether the following vectors are a basis for ℝ
^{3}. If they are, explain why they are and if they are not, give a reason and tell whether they span ℝ^{3}. - Determine whether the following vectors are a basis for ℝ
^{3}. If they are, explain why they are and if they are not, give a reason and tell whether they span ℝ^{3}. - Determine whether the following vectors are a basis for ℝ
^{3}. If they are, explain why they are and if they are not, give a reason and tell whether they span ℝ^{3}. - Consider the vectors of the form
Is this set of vectors a subspace of ℝ

^{3}? If so, explain why, give a basis for the subspace and find its dimension. - Consider the vectors of the form
Is this set of vectors a subspace of ℝ

^{4}? If so, explain why, give a basis for the subspace and find its dimension. - Consider the vectors of the form
Is this set of vectors a subspace of ℝ

^{4}? If so, explain why, give a basis for the subspace and find its dimension. - If you have 5 vectors in F
^{5}and the vectors are linearly independent, can it always be concluded they span F^{5}? Explain. - If you have 6 vectors in F
^{5}, is it possible they are linearly independent? Explain. - Suppose A is an m × n matrix and is a linearly independent set of vectors in A⊆ F
^{m}. Now suppose A= w_{i}. Showis also independent. - Suppose V,W are subspaces of F
^{n}. Show V ∩W defined to be all vectors which are in both V and W is a subspace also. - Suppose V and W both have dimension equal to 7 and they are subspaces of F
^{10}. What are the possibilities for the dimension of V ∩ W? Hint: Remember that a linear independent set can be extended to form a basis. - Suppose V has dimension p and W has dimension q and they are each contained in a subspace, U
which has dimension equal to n where n > max. What are the possibilities for the dimension of V ∩ W? Hint: Remember that a linear independent set can be extended to form a basis.
- If b≠0, can the solution set of Ax = b be a plane through the origin? Explain.
- Suppose a system of equations has fewer equations than variables and you have found a solution to this system of equations. Is it possible that your solution is the only one? Explain.
- Suppose a system of linear equations has a 2 × 4 augmented matrix and the last column is a pivot column. Could the system of linear equations be consistent? Explain.
- Suppose the coefficient matrix of a system of n equations with n variables has the property that every column is a pivot column. Does it follow that the system of equations must have a solution? If so, must the solution be unique? Explain.
- Suppose there is a unique solution to a system of linear equations. What must be true of the pivot columns in the augmented matrix.
- State whether each of the following sets of data are possible for the matrix equation Ax = b. If
possible, describe the solution set. That is, tell whether there exists a unique solution no solution or
infinitely many solutions.
- A is a 5 × 6 matrix, rank = 4 and rank= 4 . Hint: This says b is in the span of four of the columns. Thus the columns are not independent.
- A is a 3 × 4 matrix, rank = 3 and rank= 2 .
- A is a 4 × 2 matrix, rank = 4 and rank= 4 . Hint: This says b is in the span of the columns and the columns must be independent.
- A is a 5 × 5 matrix, rank = 4 and rank= 5 . Hint: This says b is not in the span of the columns.
- A is a 4 × 2 matrix, rank = 2 and rank= 2.

- A is a 5 × 6 matrix, rank
- Suppose A is an m×n matrix in which m ≤ n. Suppose also that the rank of A equals m. Show that
A maps F
^{n}onto F^{m}. Hint: The vectors e_{1},,e_{m}occur as columns in the row reduced echelon form for A. - Suppose A is an m×n matrix in which m ≥ n. Suppose also that the rank of A equals n. Show that A is one to one. Hint: If not, there exists a vector x such that Ax = 0, and this implies at least one column of A is a linear combination of the others. Show this would require the column rank to be less than n.
- Explain why an n × n matrix A is both one to one and onto if and only if its rank is n.
- Suppose A is an m × n matrix and B is an n × p matrix. Show that
Hint: Consider the subspace, B

∩ kerand suppose a basis for this subspace isNow suppose

is a basis for ker. Letbe such that Bz_{i}= w_{i}and argue thatHere is how you do this. Suppose ABx = 0. Then Bx ∈ ker

∩ Band so Bx = ∑_{i=1}^{k}Bz_{i}showing that - Explain why Ax = 0 always has a solution even when A
^{−1}does not exist.- What can you conclude about A if the solution is unique?
- What can you conclude about A if the solution is not unique?

- Let A be an n×n matrix and let x be a nonzero vector such that Ax = λx for some scalar λ. When
this occurs, the vector x is called an eigenvector and the scalar λ is called an eigenvalue. It turns
out that not every number is an eigenvalue. Only certain ones are. Why? Hint: Show that if
Ax = λx, then x = 0. Explain why this shows thatis not one to one and not onto.
- Let A be an n × n matrix and consider the matrices . Explain why there exist scalars, c
_{i}not all zero such thatThen argue there exists a polynomial, p

of the formsuch that p

= 0 and if qis another polynomial such that q= 0 , then qis of the form plfor some polynomial, l. This extra special polynomial, pis called the minimal polynomial. Hint: You might consider an n×n matrix as a vector in F^{n2 }. What would be a basis for this set of matrices?

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