Question
यदि किसी आव्यूह $A$ के लिए $A=\left[\begin{array}{cc}\alpha & -2 \\ -2 & \alpha\end{array}\right],\left|A^3\right|=125$ तब $\alpha$ का मान है $-$ 

Answer

$(A)\ \pm 3$
यहाँ $A=\left[\begin{array}{cc}\alpha & -2 \\ -2 & \alpha\end{array}\right]$ और $\left| A ^3\right|=125$
$\left| A ^n\right|=| A |^n \Rightarrow\left|A^3\right|=| A |^3$
$\Rightarrow 125=|A|^3$
$\Rightarrow 125=\left(\alpha^2-4\right)^3$
$\Rightarrow \alpha^2-4=5$
$\Rightarrow \alpha^2=9$
$\Rightarrow \alpha= \pm 3$

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