MATH 475 - Spring 2022 – Homework 0A
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MATH 475 - Spring 2022 – Homework 0A
Warm-up questions
These questions are intended to remind you of some elementary linear algebra. If you are unsure of anything, make sure to review your linear algebra notes/textbook. We will be using linear algebra throughout the course.
1. Let A, B, C, D be matrices defined by
A = '(┌)1 '(┐) , B = '(┌)4(1) '(┐) , C = '(┌)3 1'(┐) , D = ┐ .
Which of the following sums and products are well defined?
A + B A + C AB BA CD DC C≥ D≥ .
You do not need to compute these quantities.
2. Let A and B be matrices and | denote the transpose. Are the following true or false? You do not need to explain your answers.
1. (A + B)o = Ao + Bo
2. (AB)o = Ao Bo
3. (Ao)o = A
4. (λA)o = Ao, where λ is a scalar.
3. Find a matrix X that satisfies the equation B + (Tr(C)X)o = F
4. Solve the linear system
┌ ┐ ┌ ┐0(1)
11 ←2 9 2
Questions
5. Let Q ∈ Ti×i be an orthogonal matrix.
(a) What are the possible values for the eigenvalues of Q?
(b) Prove Lemma 15 from the lecture notes.
6. Let x, y ∈ Ti be nonzero vectors and consider the matrix A = xyo . What is the rank of A? What is the range R(A) and null space N (A)?
7. Let A ∈ Ti×m , where m < n and consider the linear system Ax = b. (a) How many solutions can this system have? Give an example for each case.
(b) Now let m > n. How many solutions can the linear system have in this case? Give an example for each case.
8. Let S = |x| , . . . , xm} be an orthogonal subset of Tm . Show that S is linearly independent.
9. Recall that the 1-norm and &-norms on Ti are defined by
i
|x|| = |x,|, |x|o = ,aλλxλm |x,|.
,–|
Show that each is a norm.
10. Prove Theorem 21 from the lecture notes.
2022-03-14