QUESTIONS ON SYMMETRIC AND SKEW SYMMETRIC MATRIX

About "Questions on Symmetric and Skew Symmetric Matrix"

Questions on Symmetric and Skew Symmetric Matrix :

Here we are going to see some practice questions on symmetric and skew symmetric matrix.

What is symmetric and skew symmetric matrix ?

A square matrix A is said to be symmetric if AT = A.

A square matrix A is said to be skew-symmetric if AT = −A.

Let us look into some problems to understand the concept.

Question 1 :

Construct the matrix A  =  [aij]3x3, where aij  =  i - j. State whether A is symmetric or skew-symmetric

Solution :

From the given question, we come to know that we have to construct a matrix with 3 rows and 3 columns.

i = 1, j = 1

aij  =  i - j

a11 =  1 - 1 

a11  =  0

i = 1, j = 2

aij  =  i - j

a12 =  1 - 2 

a12  =  -1

i = 1, j = 3

aij  =  i - j

a13 =  1 - 3 

a13  =  -2

i = 2, j = 1

aij  =  i - j

a21 =  2 - 1 

a21  =  1

i = 2, j = 2

aij  =  i - j

a22 =  2 - 2  

a22  =  0

i = 2, j = 3

aij  =  i - j

a23 =  2 - 3  

a23  =  -1

i = 3, j = 1

aij  =  i - j

a31 =  3 - 1 

a31  =  2

i = 3, j = 2

aij  =  i - j

a32 =  3 - 2

a32  =  1

i = 3, j = 3

aij  =  i - j

a33 =  3 - 3

a33  =  0

So, the matrix A with order 3 x 3 is

Now let us check whether it is symmetric or skew symmetric matrix.

Hence it is skew symmetric matrix.

Question 2 :

Let A and B be two symmetric matrices. Prove that AB = BA if and only if AB is a symmetric matrix.

Solution :

If A and B are symmetric matrices, then 

AT  =  A and BT  =  B

From the given question, we have to understand that we have to prove AB  =  BA if AB is symmetric matrix.

If AB is symmetric matrix, then we have to prove AB  =  BA. So, let us prove them as two cases.

Case 1 :

Prove that : AB  =  BA

Given :   AB is symmetric

If AB is symmetric,

then (AB)T  =  AB

By using transpose law,

BTAT  =  AB

(B =  B and AT  =  A)

BA  =  AB

Hence proved. 

Case 2 :

Prove that : AB is symmetric

Given :   AB  =  BA

Let us take transpose for AB

(AB)=  BT AT

(AB)T  =  BA

From the given information, AB  =  BA.So let us replace BA as AB.

(AB)T  =  AB

Hence proved.

After having gone through the stuff given above, we hope that the students would have understood "Questions on Symmetric and Skew Symmetric Matrix".

Apart from "Questions on Symmetric and Skew Symmetric Matrix" if you need any other stuff in math, please use our google custom search here.

Kindly mail your feedback to v4formath@gmail.com

We always appreciate your feedback.

©All rights reserved. onlinemath4all.com

Recent Articles

  1. De Moivre's Theorem and Its Applications

    Apr 19, 24 08:30 AM

    De Moivre's Theorem and Its Applications

    Read More

  2. First Fundamental Theorem of Calculus - Part 1

    Apr 17, 24 11:27 PM

    First Fundamental Theorem of Calculus - Part 1

    Read More

  3. Polar Form of a Complex Number

    Apr 16, 24 09:28 AM

    polarform1.png
    Polar Form of a Complex Number

    Read More