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2.1 Exercises
49
Matrix Size In Exercises 29-36, let A, B, C, D, and F
Writing a Linear Combination In Exercises 49-52,
be matrices with the sizes shown below.
write the column matrix b as a linear combination of the
A: 3 x4 B: 3 x4 C: 4 x 2 D: 4 x 2 E: 4 x 3
columns of A.
[! -1
If defined, determine the size of the matrix. If not
defined, explain why.
49. A-
-3
41
b =
3
29. A + B
30. C+E
2
31. D
32. -44
50. A =-1
2
33. AC
34. BE
35. E- 24
36. 2D +C
-5
Solving a Matrix Equation In Exercises 37 and 38,
solve the matrix equation Ax = 0.
51. A - 0 -1. b
[2
-1
37. A = *-
-3 5)
3 4
– 22]
52. A-
4
32
Solving a Matrix Equation In Exercises 53 and 54,
solve for A.
3
38. A-I -
01 -1
2
Solving a System of Linear Equations In Exercises
39-48, write the system of linear equations in the form
Ax = b and solve this matrix equation for x.
sa. ; - 1
39. -x, +x, 4
-2x, + x, =0
40. 2x, + 3x, - 5
X, + 4x, - 10
42. -4x, + 9x, --13
Solving a Matrix Equation In Exercises 55 and 56,
solve the matrix equation for a, b, e, and d.
41. -2r, - 3x, - -4
6x, + - 36
X, - 3x, = 12
43. X- 21, + 3x,- 9
-x, + 3x, - x, --6
2x, - Sx, + 5x,- 17
44. , + - 3x,- -I
Diagonal Matrix In Exercises 57 and 58, find the
product AA for the diagonal matrix. A square matrix
-A + 2x3
X - X + X, = 2
X- 5x, + 2x,--20
-3x, + X - X - 8
-2, + Sx, - - 16
... 0
... 0
a .. 0
A- 0 0
45.
0 ... a
is a diagonal matrix when all entries that are not on the
main diagonal are zero.
46. x - + 4x, - 17
K + 3x,
-6x, + Sx, -
47. 2x, - +
--||
[2 0 01
2 0 58. A - 0 -3
-1
40
57. А -
3
3x, - X, - X,--3
Finding Products of Diagonal Matrices In Exercises
59 and 60, find the products AB and BA for the diagonal
matrices.
+ ,- 3x, - -4
X, +x, + 2r,
48. X, +x,
59. A - ; - -|
X, +
3
60. A-0 -5
30
-7
B =
4
X +-0
-x, +x, - x, +x,- X= 5
12
Cecnpe pe
d dy d i
50
Chapter 2 Matrices
61. Guided Proof Prove that if A and R are diagonal
matrices (of the same size), then AB - BA.
72. Show that no ? x ? matrices A and Rexist that satisfy
the matrix equation
AB - RA -
Getting Started: To prove that the matrices AR and RA
are equal, you need to show that their corresponding
entries are equal.
(i) Begin your proof by letting A- [a,] and 8- [b,
be two diagonal nxn matrices.
73. Exploration Let i- -i and let
A - 1 and B- : 4
(ii) The ijth entry of the product AB is
(a) Find A. A'. and A. (Note: A - AA.
A - AAA = APA, and so on.) Identify any similarities
with P. P, and i.
(ii) Evaluate the entries c, for the two cases i + j and
(b) Find and identify B.