If $\left[\begin{array}{ll}2 & 1 \\ 3 & 2\end{array}\right] A\left[\begin{array}{cc}-3 & 2 \\ 5 &…
If $\left[\begin{array}{ll}2 & 1 \\ 3 & 2\end{array}\right] A\left[\begin{array}{cc}-3 & 2 \\ 5 & -3\end{array}\right]=\left[\begin{array}{ll}1 & 0 \\ 0 & 1\end{array}\right]$, then $A=$
- $\left[\begin{array}{ll}1 & 1 \\ 1 & 1\end{array}\right]$
- $\left[\begin{array}{ll}1 & 0 \\ 1 & 1\end{array}\right]$
- $\left[\begin{array}{ll}1 & 1 \\ 1 & 0\end{array}\right]$
- $\left[\begin{array}{ll}1 & 1 \\ 0 & 1\end{array}\right]$
Solution
$\begin{aligned} & {\left[\begin{array}{ll}2 & 1 \\ 3 & 2\end{array}\right] A\left[\begin{array}{cc}-3 & 2 \\ 5 & -3\end{array}\right]=\left[\begin{array}{ll}1 & 0 \\ 0 & 1\end{array}\right]} \\ & \Rightarrow A=\left[\begin{array}{ll}2 & 1 \\ 3 & 2\end{array}\right]^{-1}\left[\begin{array}{ll}1 & 0 \\ 0 & 1\end{array}\right]\left[\begin{array}{ll}3 & 2 \\ 5 & 3\end{array}\right]^{-1} \\ & \Rightarrow A=\left[\begin{array}{cc}2 & -1 \\ -3 & 2\end{array}\right]\left[\begin{array}{ll}1 & 0 \\ 0 & 1\end{array}\right]\left[\begin{array}{ll}3 & 2 \\ 5 & 3\end{array}\right] \\ & \Rightarrow A=\left[\begin{array}{cc}2 & -1 \\ -3 & 2\end{array}\right]\left[\begin{array}{ll}3 & 2 \\ 5 & 3\end{array}\right] \\ & \Rightarrow A=\left[\begin{array}{ll}1 & 1 \\ 1 & 0\end{array}\right]\end{aligned}$
Asked in: MHT CET 2022 (07 Aug Shift 1)
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