A is invertible. Is it possible for A³ to be an identity matrix without A being invertible? Explain. Can a matrix with a row of zeros or a column of zeros have an inverse? Explain.

Linear Algebra: A Modern Introduction
4th Edition
ISBN:9781285463247
Author:David Poole
Publisher:David Poole
Chapter4: Eigenvalues And Eigenvectors
Section4.2: Determinants
Problem 56EQ
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1.4 34 and 46 please on paper thanks a lot
41.
RC = tr(CR).
42. If A is a square matrix and n is a positive integer, is it true that
(A)T = (AT)"? Justify your answer.
43. a. Show that if A is invertible and AB = AC, then B = C.
b. Explain why part (a) and Example 3 do not contradict one
another.
44. Show that if A is invertible and k is any nonzero scalar, then
(KA)" = k"A" for all integer values of n.
45. a. Show that if A, B, and A + B are invertible matrices with
the same size, then
A(A¯¹ + B¯¹)B(A + B)-¹ = I
b. What does the result in part (a) tell you about the matrix
A¹+B-¹?
46. A square matrix A is said to be idempotent if A² = A.
a. Show that if A is idempotent, then so is I - A.
b. Show that if A is idempotent, then 2A - I is invertible and
is its own inverse.
47. Show that if A is a square matrix such that Ak = 0 for some
positive integer k, then the matrix I-A is invertible and
(I - A)¹ = I + A + A²+
+ Ak-1
48. Show that the matrix
^=[ 2
A
satisfies the equation
A² - (a + d)A + (ad - bc)I = 0
49, Assuming that all matrices are nxn and invertible, solve
Transcribed Image Text:41. RC = tr(CR). 42. If A is a square matrix and n is a positive integer, is it true that (A)T = (AT)"? Justify your answer. 43. a. Show that if A is invertible and AB = AC, then B = C. b. Explain why part (a) and Example 3 do not contradict one another. 44. Show that if A is invertible and k is any nonzero scalar, then (KA)" = k"A" for all integer values of n. 45. a. Show that if A, B, and A + B are invertible matrices with the same size, then A(A¯¹ + B¯¹)B(A + B)-¹ = I b. What does the result in part (a) tell you about the matrix A¹+B-¹? 46. A square matrix A is said to be idempotent if A² = A. a. Show that if A is idempotent, then so is I - A. b. Show that if A is idempotent, then 2A - I is invertible and is its own inverse. 47. Show that if A is a square matrix such that Ak = 0 for some positive integer k, then the matrix I-A is invertible and (I - A)¹ = I + A + A²+ + Ak-1 48. Show that the matrix ^=[ 2 A satisfies the equation A² - (a + d)A + (ad - bc)I = 0 49, Assuming that all matrices are nxn and invertible, solve
29. The matrix A in Exercise 21.
30. An arbitrary square matrix A.
31. a. Give an example of two 2 x 2 matrices such that
(A + B)(A - B) # A² - B²
b. State a valid formula for multiplying out
(A + B)(A - B)
c. What condition can you impose on A and B that will allow
you to write (A + B)(A - B) = A² - B²?
32. The numerical equation a² : = 1 has exactly two solutions. Find
at least eight solutions of the matrix equation A² = 13. [Hint:
Look for solutions in which all entries off the main diagonal
are zero.]
4
33. a. Show that if a square matrix A satisfies the equation
A² + 2A + I = 0, then A must be invertible. What is the
inverse?
b. Show that if p(x) is a polynomial with a nonzero constant
term, and if A is a square matrix for which p(A) = 0, then
A is invertible.
34. Is it possible for A³ to be an identity matrix without A being
invertible? Explain.
35. Can a matrix with a row of zeros or a column of zeros have an
inverse? Explain.
a.
b
47.
48.
Transcribed Image Text:29. The matrix A in Exercise 21. 30. An arbitrary square matrix A. 31. a. Give an example of two 2 x 2 matrices such that (A + B)(A - B) # A² - B² b. State a valid formula for multiplying out (A + B)(A - B) c. What condition can you impose on A and B that will allow you to write (A + B)(A - B) = A² - B²? 32. The numerical equation a² : = 1 has exactly two solutions. Find at least eight solutions of the matrix equation A² = 13. [Hint: Look for solutions in which all entries off the main diagonal are zero.] 4 33. a. Show that if a square matrix A satisfies the equation A² + 2A + I = 0, then A must be invertible. What is the inverse? b. Show that if p(x) is a polynomial with a nonzero constant term, and if A is a square matrix for which p(A) = 0, then A is invertible. 34. Is it possible for A³ to be an identity matrix without A being invertible? Explain. 35. Can a matrix with a row of zeros or a column of zeros have an inverse? Explain. a. b 47. 48.
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