3 and 4 .Determinants and Matrices
medium

અહી $I$ એ $2 \times 2$ કક્ષાનો  એકમ શ્રેણીક છે અને  $P=\left[\begin{array}{cc}2 & -1 \\ 5 & -3\end{array}\right] $ છે. તો $n \in N$ ની કિમંત મેળવો કે જેથી $P^n =5 I -8 P$ થાય.

A

$8$

B

$10$

C

$4$

D

$6$

(JEE MAIN-2021)

Solution

$P=\left[\begin{array}{cc}2 & -1 \\ 5 & -3\end{array}\right]$

$5 I-8 P=\left[\begin{array}{ll}5 & 0 \\ 0 & 5\end{array}\right]-\left[\begin{array}{cc}16 & -8 \\ 40 & -24\end{array}\right]=\left[\begin{array}{ll}-11 & 8 \\ -40 & 29\end{array}\right]$

$P^{2}=\left[\begin{array}{ll}-1 & 1 \\ -5 & 4\end{array}\right]$

$P^{3}=\left[\begin{array}{cc}3 & -2 \\ 10 & -7\end{array}\right] \Rightarrow P^{6}=\left[\begin{array}{ll}-11 & 8 \\ -40 & 29\end{array}\right]=P^{n}$

$\Rightarrow n=6$

Standard 12
Mathematics

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