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3 and 4 .Determinants and Matrices
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माना I, कोटि $2 \times 2$ का तत्समक आव्यूह है तथा $P =\left[\begin{array}{rr}2 & -1 \\ 5 & -3\end{array}\right]$ है। तो $n \in N$ का वह मान, जिसके लिए $Pn =5 I -8 P$ है, बराबर है
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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