Page 1
7. Adjoint and Inverse of a Matrix
Exercise 7.1
1 A. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
= 4
C
12
= – 2
C
21
= – 5
C
22
= – 3
Since, adj A =
(adj A) =
=
Now, (adj A)A =
(adj A)A =
And, |A|.I =
Also, A(adj A) =
A(adj A) =
Hence, (adj A)A = |A|.I = A.(adj A)
1 B. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Page 2
7. Adjoint and Inverse of a Matrix
Exercise 7.1
1 A. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
= 4
C
12
= – 2
C
21
= – 5
C
22
= – 3
Since, adj A =
(adj A) =
=
Now, (adj A)A =
(adj A)A =
And, |A|.I =
Also, A(adj A) =
A(adj A) =
Hence, (adj A)A = |A|.I = A.(adj A)
1 B. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
= d
C
12
= – c
C
21
= – b
C
22
= a
Since, adj A =
(adj A) =
=
Now, (adj A)A =
(adj A)A =
And, |A|.I =
Also, A(adj A) =
Hence, (adj A)A = |A|.I = A.(adj A)
1 C. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
=
C
12
=
C
21
=
C
22
=
Since, adj A =
(adj A) =
=
Page 3
7. Adjoint and Inverse of a Matrix
Exercise 7.1
1 A. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
= 4
C
12
= – 2
C
21
= – 5
C
22
= – 3
Since, adj A =
(adj A) =
=
Now, (adj A)A =
(adj A)A =
And, |A|.I =
Also, A(adj A) =
A(adj A) =
Hence, (adj A)A = |A|.I = A.(adj A)
1 B. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
= d
C
12
= – c
C
21
= – b
C
22
= a
Since, adj A =
(adj A) =
=
Now, (adj A)A =
(adj A)A =
And, |A|.I =
Also, A(adj A) =
Hence, (adj A)A = |A|.I = A.(adj A)
1 C. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
=
C
12
=
C
21
=
C
22
=
Since, adj A =
(adj A) =
=
Now, (adj A)A =
(adj A)A =
And, |A|.I =
=
=
=
Also, A(adj A) =
=
Hence, (adj A)A = |A|.I = A.(adj A)
1 D. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
= 1
C
12
=
C
21
=
C
22
= 1
Since, adj A =
(adj A) =
=
Page 4
7. Adjoint and Inverse of a Matrix
Exercise 7.1
1 A. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
= 4
C
12
= – 2
C
21
= – 5
C
22
= – 3
Since, adj A =
(adj A) =
=
Now, (adj A)A =
(adj A)A =
And, |A|.I =
Also, A(adj A) =
A(adj A) =
Hence, (adj A)A = |A|.I = A.(adj A)
1 B. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
= d
C
12
= – c
C
21
= – b
C
22
= a
Since, adj A =
(adj A) =
=
Now, (adj A)A =
(adj A)A =
And, |A|.I =
Also, A(adj A) =
Hence, (adj A)A = |A|.I = A.(adj A)
1 C. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
=
C
12
=
C
21
=
C
22
=
Since, adj A =
(adj A) =
=
Now, (adj A)A =
(adj A)A =
And, |A|.I =
=
=
=
Also, A(adj A) =
=
Hence, (adj A)A = |A|.I = A.(adj A)
1 D. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
= 1
C
12
=
C
21
=
C
22
= 1
Since, adj A =
(adj A) =
=
Now, (adj A)A =
=
(adj A)A =
And, |A|.I =
=
Also, A(adj A) =
=
=
Hence, (adj A)A = |A|.I = A.(adj A)
2 A. Question
Find the adjoint of each of the following Matrices and Verify that (adj A) A = |A| I = A (adj A)
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are:
C
11
= – 3 C
21
= 2 C
31
= 2
C
12
= 2 C
22
= – 3 C
23
= 2
C
13
= 2 C
23
= 2 C
33
= – 3
adj A =
=
Page 5
7. Adjoint and Inverse of a Matrix
Exercise 7.1
1 A. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
= 4
C
12
= – 2
C
21
= – 5
C
22
= – 3
Since, adj A =
(adj A) =
=
Now, (adj A)A =
(adj A)A =
And, |A|.I =
Also, A(adj A) =
A(adj A) =
Hence, (adj A)A = |A|.I = A.(adj A)
1 B. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
= d
C
12
= – c
C
21
= – b
C
22
= a
Since, adj A =
(adj A) =
=
Now, (adj A)A =
(adj A)A =
And, |A|.I =
Also, A(adj A) =
Hence, (adj A)A = |A|.I = A.(adj A)
1 C. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
=
C
12
=
C
21
=
C
22
=
Since, adj A =
(adj A) =
=
Now, (adj A)A =
(adj A)A =
And, |A|.I =
=
=
=
Also, A(adj A) =
=
Hence, (adj A)A = |A|.I = A.(adj A)
1 D. Question
Find the adjoint of each of the following Matrices.
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are
C
11
= 1
C
12
=
C
21
=
C
22
= 1
Since, adj A =
(adj A) =
=
Now, (adj A)A =
=
(adj A)A =
And, |A|.I =
=
Also, A(adj A) =
=
=
Hence, (adj A)A = |A|.I = A.(adj A)
2 A. Question
Find the adjoint of each of the following Matrices and Verify that (adj A) A = |A| I = A (adj A)
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A are:
C
11
= – 3 C
21
= 2 C
31
= 2
C
12
= 2 C
22
= – 3 C
23
= 2
C
13
= 2 C
23
= 2 C
33
= – 3
adj A =
=
Now, (adj A).A =
=
=
Also, |A|.I = = ( – 3 + 4 + 4)
=
Then, A.(adj A) =
=
=
Since, (adj A).A = |A|.I = A(adj A)
2 B. Question
Find the adjoint of each of the following Matrices and Verify that (adj A) A = |A| I = A (adj A)
Verify that (adj A) A=|A| I=A (adj A) for the above matrices.
Answer
A =
Cofactors of A
C
11
= 2 C
21
= 3 C
31
= – 13
C
12
= – 3 C
22
= 6 C
32
= 9
C
13
= 5 C
23
= – 3 C
33
= – 1
adj A =
=
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