M340L Exam 3A: Linear Algebra Problems - Prof. Arlo W. Schurle, Exams of Mathematics

The solutions manual for exam 3a of a linear algebra course, including problems on eigenvalues, eigenvectors, orthonormal matrices, and linear transformations.

Typology: Exams

Pre 2010

Uploaded on 05/23/2010

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M340L EXAM 3A Your name:
SPRING, 2010
Dr. Schurle Your UTEID:
Show all your work on these pages. Be organized and neat. Your work should be your
own; there should be no talking, reading notes, checking laptops, using cellphones, .. . .
1. (10 points) Suppose the matrix Ahas eigenvalues 3 and 5 with corresponding eigen-
vectors v1and v2. Using only algebra and definitions, show why v1and v2are linearly
independent.
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M340L EXAM 3A Your name: SPRING, 2010 Dr. Schurle Your UTEID:

Show all your work on these pages. Be organized and neat. Your work should be your own; there should be no talking, reading notes, checking laptops, using cellphones,....

  1. (10 points) Suppose the matrix A has eigenvalues 3 and 5 with corresponding eigen- vectors v 1 and v 2. Using only algebra and definitions, show why v 1 and v 2 are linearly independent.

YOUR SCORE: /

  1. (10 points) Suppose the columns of a matrix U are orthonormal. Explain why U T^ U = I, where I is the identity matrix of the appropriate size, and then why (U x) · (U y) = x · y for vectors x and y of the appropriate size.
  2. (8 points) Is v =

  

   an eigenvector of the matrix

  

  ? If so, what is

its eigenvalue? If not, explain why not.

  1. Remember that P 2 is the vector space of all polynomials of degree no more than 2. Suppose T : P 2 → P 2 is the linear transformation given by T (p(t)) = 2tp′(t) + 3p(t), where p′(t) is the derivative of p(t).

(a) (4 points) Calculate and simplify T (2t^2 + 3t − 1).

(b) (8 points) What is the matrix for T relative to the standard basis for P 2?

(c) (8 points) What is the matrix for T relative to the basis B = { 1 , t − 1 , (t − 1)^2 }?

  1. Let W be the subspace of R^4 spanned by the vectors u 1 , u 2 , u 3 , where

u 1 =

  

   , u 2 =

  

   , u 3 =

  

  .

(a) (4 points) Verify that {u 1 , u 2 , u 3 } is an orthogonal basis for W.

(b) (10 pts.) Find (and simplify) the vector in W that is closest to y =

  

  .

(c) (6 points) Find the distance between y and the vector in W that is closest to y.

(d) (6 points) Find a nonzero vector in W ⊥.