Let $\mathrm{A}$ and $\mathrm{B}$ be any two $3 \times 3$ symmetric and skew symmetric matrices respectively. Then which of the following is NOT true?
Solution
<p>(A) $M = {A^4} - {B^4}$</p>
<p>${M^T} = {({A^4} - {B^4})^T} = {({A^T})^4} - {({B^T})^4}$</p>
<p>$= {A^4} - {( - B)^4} = {A^4} - {B^4} = M$</p>
<p>(B) $M = AB - BA$</p>
<p>${M^T} = {(AB - BA)^T} = {(AB)^T} - {(BA)^T}$</p>
<p>$= {B^T}{A^T} - {A^T}{B^T}$</p>
<p>$= - BA - A( - B)$</p>
<p>$= AB - BA = M$</p>
<p>(C) $M = {B^5} - {A^5}$</p>
<p>${M^T} = {({B^T})^5} - {({A^T})^5} = - ({B^5} + {A^5}) \ne - M$</p>
<p>(D) $M = AB + BA$</p>
<p>${M^T} = {(AB)^T} + {(BA)^T}$</p>
<p>$= {B^T}{A^T} + {A^T}{B^T} = - BA - AB = - M$</p>
About this question
Subject: Mathematics · Chapter: Matrices and Determinants · Topic: Types of Matrices and Operations
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