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QJEEM25Maa5d9: JEE Main 2025 Mathematics - Class 12 JEEM25Maa5d9 Solution: Let , where . Then is equal to __________.

Let S={m∈Z:Am2+Am=3I−A−6}S=\left\{m \in \mathbf{Z}: A^{m^2}+A^m=3 I-A^{-6}\right\} , where A=[2amp;−11amp;0]A=\left[\begin{array}{cc}2 & -1 \\ 1 & 0\end{array}\right] . Then n(S)n(S) is equal to __________.

Step-by-Step Verified Solution

amp;amp;A=[2amp;−11amp;0]amp;A2=[3amp;−22amp;−1],A3=[4amp;−33amp;−2],A4=[5amp;−44amp;−3]amp; and so on amp;amp;A6=[7amp;−66amp;−5]amp;Am=[m+1amp;−m mamp;−m+1],amp;Am2=[m2+1amp;−m2 m2amp;−(m2−1)]amp;Am2+Am=3I−A−6amp;[m2+1amp;−m2 m2amp;−(m2−1)]+[m+1amp;−m mamp;−m+1]\begin{aligned}&\begin{aligned}& A=\left[\begin{array}{cc}2 & -1 \\1 & 0\end{array}\right] \\& A^2=\left[\begin{array}{ll}3 & -2 \\2 & -1\end{array}\right], A^3=\left[\begin{array}{ll}4 & -3 \\3 & -2\end{array}\right], A^4=\left[\begin{array}{ll}5 & -4 \\4 & -3\end{array}\right]\end{aligned}\\&\text { and so on }\\&\begin{aligned}& \mathrm{A}^6=\left[\begin{array}{ll}7 & -6 \\6 & -5\end{array}\right] \\& \mathrm{A}^{\mathrm{m}}=\left[\begin{array}{cc}\mathrm{m}+1 & -\mathrm{m} \\\mathrm{~m} & -\mathrm{m}+1\end{array}\right], \\& \mathrm{A}^{\mathrm{m}^2}=\left[\begin{array}{cc}\mathrm{m}^2+1 & -\mathrm{m}^2 \\\mathrm{~m}^2 & -\left(\mathrm{m}^2-1\right)\end{array}\right] \\& \mathrm{A}^{\mathrm{m}^2}+\mathrm{A}^{\mathrm{m}}=3 \mathrm{I}-\mathrm{A}^{-6} \\& {\left[\begin{array}{cc}\mathrm{m}^2+1 & -\mathrm{m}^2 \\\mathrm{~m}^2 & -\left(\mathrm{m}^2-1\right)\end{array}\right]+\left[\begin{array}{cc}\mathrm{m}+1 & -\mathrm{m} \\\mathrm{~m} & -\mathrm{m}+1\end{array}\right]}\end{aligned}\end{aligned}

amp;=3[1amp;00amp;1]−[−5amp;6−6amp;7]amp;=[8amp;−66amp;−4]amp;=m2+1+m+1=8amp;=m2+m−6=0⇒ m=−3,2amp;n( s)=2\begin{aligned}& =3\left[\begin{array}{ll}1 & 0 \\0 & 1\end{array}\right]-\left[\begin{array}{ll}-5 & 6 \\-6 & 7\end{array}\right] \\& =\left[\begin{array}{ll}8 & -6 \\6 & -4\end{array}\right] \\& =\mathrm{m}^2+1+\mathrm{m}+1=8 \\& =\mathrm{m}^2+\mathrm{m}-6=0 \Rightarrow \mathrm{~m}=-3,2 \\& \mathrm{n}(\mathrm{~s})=2\end{aligned}

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