Target Exam

CUET

Subject

-- Applied Mathematics - Section B2

Chapter

Algebra

Question:

Let $A=[a_{ij}]$ be $2 × 2 $ matrix, where $aij=\left\{\begin{matrix}1 & i≠j\\0 & i=j \end{matrix}\right.$, then

Options:

$A^{22}-A^7+A=I$

$A^{23}-A^7+A=I$

$A^{22}-A^8+A=I$

$A^{23}-A^8-A=I$

Correct Answer:

$A^{22}-A^7+A=I$

Explanation:

The correct answer is Option (1) → $A^{22}-A^7+A=I$

$A=\begin{bmatrix}0&1\\1&0\end{bmatrix}$  [Given]

$⇒A^2=\begin{bmatrix}0&1\\1&0\end{bmatrix}\begin{bmatrix}0&1\\1&0\end{bmatrix}=\begin{bmatrix}1&0\\0&1\end{bmatrix}$

$⇒A^2=I$

$(A^2)^{11}=I^{11}$  $[I^n=I]$

$A^{22}=I$

Now,

$A^7=\begin{bmatrix}0&1\\1&0\end{bmatrix}$

$∴A^{22}-A^7=\begin{bmatrix}1&-1\\-1&1\end{bmatrix}$

$⇒A^{22}-A^7+A=\begin{bmatrix}1&-1\\-1&1\end{bmatrix}+\begin{bmatrix}0&1\\1&0\end{bmatrix}$

$=\begin{bmatrix}1&0\\0&1\end{bmatrix}=I$