ve Theorem 4 for A 25. Show that if ad bc = 0, then the equation Ax = 0 has more than one solution. Why does this imply that A is not invertible? [Hint: First, consider a = b = 0. Then, if a and - 36. [L th

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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Question

25

17. Solve the equation AB = BC for A, assuming
Care square and B is invertible.
18. Suppose P is invertible and A = PBP-1. Solve for B in
terms of A.
19. If A, B, and C are n x n invertible matrices, does the equation
C-¹(A + X)B¯¹ = 1, have a solution, X? If so, find it.
20. Suppose A, B, and X are nxn matrices with A, X, and
A - AX invertible, and suppose
(A - AX)¹ = X-¹ B
a. Explain why B is invertible.
b. Solve (3) for X. If you need to invert a matrix, explain
why that matrix is invertible.
(3)
22. Explain why the columns of an n x n matrix A span R" when
A is invertible. [Hint: Review Theorem 4 in Section 1.4.]
21. Explain why the columns of an n x n matrix A are linearly 34. Repeal
independent when A is invertible.
23. Suppose A is n x n and the equation Ax = 0 has only the
trivial solution. Explain why A has n pivot columns and A is
row equivalent to I. By Theorem 7, this shows that A must
be invertible. (This exercise and Exercise 24 will be cited in
Section 2.3.)
24. Suppose A is n x n and the equation Ax = b has a solution
for each b in R". Explain why A must be invertible. [Hint: Is
A row equivalent to I,?]
Exercises 25 and 26 prove Theorem 4 for A =
а
-[²2]
C
d
25. Show that if ad - bc = 0, then the equation Ax = 0 has
more than one solution. Why does this imply that A is not
invertible? [Hint: First, consider a = b = 0. Then, if a and
-b
b are not both zero, consider the vector x =
a
26. Show that if ad - bc #0, the formula for A-1
works.
1
31. X-23
33. Use the
Exercises 27 and 28 prove special cases of the facts about elemen-
tary matrices stated in the box following Example 5. Here A is a
Let A
inverse
and Br
A =
correc
35. Let A
38.
witho
36. [M] L
third
37. Let
error
Com
Transcribed Image Text:17. Solve the equation AB = BC for A, assuming Care square and B is invertible. 18. Suppose P is invertible and A = PBP-1. Solve for B in terms of A. 19. If A, B, and C are n x n invertible matrices, does the equation C-¹(A + X)B¯¹ = 1, have a solution, X? If so, find it. 20. Suppose A, B, and X are nxn matrices with A, X, and A - AX invertible, and suppose (A - AX)¹ = X-¹ B a. Explain why B is invertible. b. Solve (3) for X. If you need to invert a matrix, explain why that matrix is invertible. (3) 22. Explain why the columns of an n x n matrix A span R" when A is invertible. [Hint: Review Theorem 4 in Section 1.4.] 21. Explain why the columns of an n x n matrix A are linearly 34. Repeal independent when A is invertible. 23. Suppose A is n x n and the equation Ax = 0 has only the trivial solution. Explain why A has n pivot columns and A is row equivalent to I. By Theorem 7, this shows that A must be invertible. (This exercise and Exercise 24 will be cited in Section 2.3.) 24. Suppose A is n x n and the equation Ax = b has a solution for each b in R". Explain why A must be invertible. [Hint: Is A row equivalent to I,?] Exercises 25 and 26 prove Theorem 4 for A = а -[²2] C d 25. Show that if ad - bc = 0, then the equation Ax = 0 has more than one solution. Why does this imply that A is not invertible? [Hint: First, consider a = b = 0. Then, if a and -b b are not both zero, consider the vector x = a 26. Show that if ad - bc #0, the formula for A-1 works. 1 31. X-23 33. Use the Exercises 27 and 28 prove special cases of the facts about elemen- tary matrices stated in the box following Example 5. Here A is a Let A inverse and Br A = correc 35. Let A 38. witho 36. [M] L third 37. Let error Com
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