Determinants - Linear Algebra - Exam, Exams of Linear Algebra

This is the Exam of Linear Algebra which includes Encouraged, Vectors, System, Method, Factorization, Square Matrices, Throughout, Invertible, Symmetric etc. Key important points are: Determinants, Properties, Obtained, Interchanging, Invertible, Factorization, Equation, Formula, Invertible, Using Pivots

Typology: Exams

2012/2013

Uploaded on 02/27/2013

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Math 205 Section B
Test 2 (50 points)
Name:
Check that you have 6 questions on three pages.
Show all your work to receive full credit for a problem.
1. (10 points) Let Aand Bbe 4×4 matrices, with det A=10 and det B= 6. Use properties
of determinants to compute:
(a) det A2BT
(b) det 2B
(c) det Cwhere Cis obtained from Aby interchanging rows 2 and 4
(d) det (B2)1if B2is invertible. Otherwise, explain why B2is not invertible.
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Math 205 Section B

Test 2 (50 points)

Name:

  • Check that you have 6 questions on three pages.
  • Show all your work to receive full credit for a problem.
  1. (10 points) Let A and B be 4 × 4 matrices, with det A = −10 and det B = 6. Use properties of determinants to compute: (a) det A^2 BT

(b) det 2B

(c) det C where C is obtained from A by interchanging rows 2 and 4

(d) det (B^2 )−^1 if B^2 is invertible. Otherwise, explain why B^2 is not invertible.

  1. (8 points) Let A =

[ 2 4 − 2

]

(a) Find an LU factorization of A.

(b) Use the LU factorization in part (a) to solve the equation A~x =

[ 1

]

  1. (8 points) Supose a 5 × 5 matrix A is invertible. Explain (using pivots) why the columns of A are linearly independent. (If you find it helpful, you may use the following steps in your explanation.)

Since A is invertible, A reduces to.

So the number of pivots in A is

Use this to explain why the columns of A are linearly independent.

  1. (8 points) Determine if each of the following sets is a subspace of the appropriate vector space.

(a) Let W =

a b a + b

 (^) : a, b are real numbers.

. Is^ W^ a subspace of^ R

(^3)? Explain.

(b) Let W be the set of all polynomials of the form p(t) = t + a where a is a real number. Is W a subspace of P 1? Explain. (P 1 is the set of all polynomials of degree atmost one.)