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Solutions 3. Matrices - Exercise 3.3 | Class 12 Mathematics-I - Toppers Study

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Solutions 3. Matrices - Exercise 3.3 | Class 12 Mathematics-I - Toppers Study

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Chapter 3 Mathematics-I class 12

Exercise 3.3 class 12 Mathematics-I Chapter 3. Matrices

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  • Solutions 3. Matrices - Exercise 3.3 | Class 12 Mathematics-I - Toppers Study
  • Class 12 Ncert Solutions
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  • Solutions Class 12
  • Chapter 3. Matrices Exercise 3.3 Class 12

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3. Matrices

| Exercise 3.3 |

Solutions 3. Matrices - Exercise 3.3 | Class 12 Mathematics-I - Toppers Study


Exercise 3.3

Ques.1. Find the transpose of each of the following matrices:

(i) 

(ii) 

(iii)  

Ans. (i) Let A = 

  Transpose of A = A’ or AT = 

(ii) 

  Transpose of A = A’ or AT = 

(iii) 

  Transpose of A = A’ or AT = 

 

 

Ques.2. If A =  and B =  then verify that:

(i) 

(ii) 

Ans. (i) A + B =  =  = 

L.H.S. = (A + B)’ =  = 

R.H.S. = A’ + B’ = 

 = 

 =  = 

  L.H.S. = R.H.S.        

hance Proved.

(ii) A – B =  

 = 

L.H.S. = (A – B)’ =  = 

R.H.S. = A’ – B’ = 

 = 

  =  = 

  L.H.S. = R.H.S.        

hance Proved.


 

Ques.3. If A’ =  and B =  then verify that:

(i) 

(ii) 

Ans. Given: A’ =  and B =  then (A’)’ = A = 

(i) A + B =  

  L.H.S. = (A + B)’ = 

R.H.S. = A’ + B’

 

 = 

  L.H.S. = R.H.S.        

hance Proved.

(ii) A – B =  

  L.H.S. = (A – B)’

R.H.S. = A’ – B’

 

 = 

  L.H.S. = R.H.S.        

hance Proved.

 

 

Ques.4. If A’ =  and B =  then find (A + 2B)’.

Ans. Given: A’ =  and B =  then (A’)’ = A = 

A +2B =  

 ]

 = 

  (A + 2B)’ = 

 

 

Ques.5. For the matrices A and B, verify that (AB)’ = B’A’, where:

(i) A =  B = 

(ii) A =  B =  

Ans. (i) AB =  = 

  L.H.S. = (AB)’

 = 

R.H.S. = B’A’

 

 

  L.H.S. = R.H.S.        

hance Proved.

(ii) AB =  = 

  L.H.S. = (AB)’

R.H.S. = B’A’

 

 

  L.H.S. = R.H.S.        

hance Proved.

 

 

Ques.6. (i) If A =  then verify that A’A = I.

(ii) If A =  then verify that A’A = I.

Ans. (i) L.H.S. = A’A = 

 =  = I = R.H.S.

(ii) L.H.S. = A’A

 

 =  

= I = R.H.S.

 

 

Ques.7. (i) Show that the matrix A =  is a symmetric matrix.

(ii) Show that the matrix A =  is a skew symmetric matrix.

Ans. (i) Given: A =   ……….(i)

Changing rows of matrix A as the columns of new matrix A’ =  = A

  A’ = A

hance, by definitions of symmetric matrix, A is a symmetric matrix.

(ii) Given: A =  ……….(i)

  A’ =  

Taking  common, A’ =  = – A   [From eq. (i)]

hance, by definition matrix A is a skew-symmetric matrix

 

 

Ques.8. For a matrix A =  verify that:

(i) (A + A’) is a symmetric matrix.

(ii) (A – A’) is a skew symmetric matrix.

Ans. (i) Given: A = 

Let B = A + A’ =  

 

  B’ =  = B

  B = A + A’ is a symmetric matrix.

(ii) Given: 

Let B = A – A’ =  

 

 B’ = 

Taking  common,  = – B

  B = A – A’ is a skew-symmetric matrix.

 

Ques.9. Find  (A + A’) and  (A – A’) when A =  

Ans. Given: A =      A’ = 

Now, A + A’ =  =  = 

   (A + A’) = 

Now, A – A’ =  =  = 

   (A – A’) =  = 

 

 

Ques.10. Express the following matrices as the sum of a symmetric and skew symmetric matrix:

(i) 

(ii) 

(iii) 

(iv)  

Ans. (i) Given:  A =     so,  A’ = 

 Symmetric matrix =  (A + A’)

 = 

Skew symmetric matrix =  (A – A’)

 = 

 Given matrix A is sum of Symmetric matrix  and Skew symmetric matrix .

(ii) Given: A =    so, A’ = 

  Symmetric matrix =  (A + A’)

 = 

And Skew symmetric matrix =  (A – A’)

 = 

 Given matrix A is sum of Symmetric matrix  and Skew symmetric  matrix .

(iii) Given: A =    so,  A’ = 

 Symmetric matrix =  (A + A’)

 = 

And Skew symmetric matrix =  (A–A’)

 = 

Given matrix A is sum of Symmetric matrix  and Skew symmetric  matrix .

(iv) Given: A =     so, A’ = 

  Symmetric matrix =  (A + A’)

 

 = 

And Skew symmetric matrix =  (A – A’)

 

 Given matrix A is sum of Symmetric matrix  and Skew symmetric matrix .

 

 

Ques.11. If A and B are symmetric matrices of same order, AB – BA is a:

(A) Skew-symmetric matrix

(B) Symmetric matrix

(C) Zero matrix

(S) Identity matrix

Ans. Given: A and B are symmetric matrices   A = A’ and B = B’

Now, (AB – BA)’ = (AB)’ – (BA)’  

 (AB – BA)’ = B’A’ – A’B’ [Reversal law]

 (AB – BA)’ = BA – AB [From eq. (i)]

 (AB – BA)’ = – (AB – BA)

  (AB – BA) is a skew matrix.

hance, option (A) is correct.

 

 

Ques.12. If A = , then A + A’ = I, if the value of  is:

(A) 

(B) 

(C) 

(D)  

Ans. Given: A =   Also A + A’ = I

     

Equating corresponding entries, we have

  

   

  

 

hance, option (B) is correct.

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