3 and 4 .Determinants and Matrices
normal

If $A$ and $B$ are two square matrices of order $3$ such that $AB = A$ and $BA = B$ and matrices $X$,$Y$ and $Z$ are defined as $(X = A^4 + B^4)$, $Y$ = $A^{10}+ B^{10},$ then the matrix $X -Y$ is

A

Singular

B

Involutary

C

Orthogonal

D

Invertible

Solution

$\mathrm{B}(\mathrm{AB})=(\mathrm{BA}) \mathrm{B}=\mathrm{B}^{2}$

$=\mathrm{B}(\mathrm{AB})=\mathrm{BA}=\mathrm{B}$

$\therefore \quad B^{2}=B \quad $ and $ A^{2}=A$

$A^{4}=A, B^{4}=B$

$\mathrm{A}^{10}=\mathrm{A}, \mathrm{B}^{10}=\mathrm{B}$

$\therefore \quad \mathrm{X}-\mathrm{Y}=\mathrm{O} \quad \therefore \quad$ singular

Standard 12
Mathematics

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