25. A is a 4 x 4 matrix with three eigenvalues. One eigenspace is one-dimensional, and one of the other eigenspaces is two- dimensional. Is it possible that A is not diagonalizable? Justify your answer.

Linear Algebra: A Modern Introduction
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Chapter5: Orthogonality
Section5.3: The Gram-schmidt Process And The Qr Factorization
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ces.
tudy
fore
5.3 Diagonalization 289
24. A is a 3 x 3 matrix with two eigenvalues. Each eigenspace is
one-dimensional. Is A diagonalizable? Why?
25. A is a 4 x 4 matrix with three eigenvalues. One eigenspace
is one-dimensional, and one of the other eigenspaces is two-
dimensional. Is it possible that A is not diagonalizable?
Justify your answer.
26. A is a 7 x 7 matrix with three eigenvalues. One eigenspace is
two-dimensional, and one of the other eigenspaces is three-
dimensional. Is it possible that A is not diagonalizable?
Justify your answer.
27. Show that if A is both diagonalizable and invertible, then so
is A-¹.
28. Show that if A has n linearly independent eigenvectors, then
so does AT. [Hint: Use the Diagonalization Theorem.]
29. A factorization A = PDP is not unique. Demonstrate this
3
for the matrix A in Example 2. With D₁ =
[³
0
0
9]
5
the information in Example 2 to find a matrix P₁ such that
A = P₁D₁P₁¯¯¹.
use
-1
30. With A and D as in Example 2, find an invertible P₂ unequal
to the P in Example 2, such that A = P₂DP₂¹.
742
31. Construct a nonzero 2 x 2 matrix that is invertible but not
diagonalizable.
32. Construct a nondiagonal 2 × 2 matrix that is diagonalizable
but not invertible.
[M] Diagonalize the matrices in Exercises 33-36. Use your ma-
's eigenvalue command to find the eigenvalues, and
as in Section 5.1.
Transcribed Image Text:ces. tudy fore 5.3 Diagonalization 289 24. A is a 3 x 3 matrix with two eigenvalues. Each eigenspace is one-dimensional. Is A diagonalizable? Why? 25. A is a 4 x 4 matrix with three eigenvalues. One eigenspace is one-dimensional, and one of the other eigenspaces is two- dimensional. Is it possible that A is not diagonalizable? Justify your answer. 26. A is a 7 x 7 matrix with three eigenvalues. One eigenspace is two-dimensional, and one of the other eigenspaces is three- dimensional. Is it possible that A is not diagonalizable? Justify your answer. 27. Show that if A is both diagonalizable and invertible, then so is A-¹. 28. Show that if A has n linearly independent eigenvectors, then so does AT. [Hint: Use the Diagonalization Theorem.] 29. A factorization A = PDP is not unique. Demonstrate this 3 for the matrix A in Example 2. With D₁ = [³ 0 0 9] 5 the information in Example 2 to find a matrix P₁ such that A = P₁D₁P₁¯¯¹. use -1 30. With A and D as in Example 2, find an invertible P₂ unequal to the P in Example 2, such that A = P₂DP₂¹. 742 31. Construct a nonzero 2 x 2 matrix that is invertible but not diagonalizable. 32. Construct a nondiagonal 2 × 2 matrix that is diagonalizable but not invertible. [M] Diagonalize the matrices in Exercises 33-36. Use your ma- 's eigenvalue command to find the eigenvalues, and as in Section 5.1.
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