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If A=[31−12]A = \begin{bmatrix} 3 & 1 \\ -1 & 2 \end{bmatrix}, then A2−5AA^2 - 5A is equal to : (where I2I_2 is identity matrix of order 2)

Solution

✅ Correct Option: 1

A2=[85−53]A^2=\begin{bmatrix}8&5\\-5&3\end{bmatrix} and 5A=[155−510]5A=\begin{bmatrix}15&5\\-5&10\end{bmatrix}. Subtracting, A2−5A=[−700−7]=−7I2A^2-5A=\begin{bmatrix}-7&0\\0&-7\end{bmatrix}=-7I_2.

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