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Exercise 7.5 · Q5

Q.If A=[λ1−1−λ]A = \begin{bmatrix} \lambda & 1 \\ -1 & -\lambda \end{bmatrix}, then for what value of λ\lambda, A2=OA^2 = O?

(1) 00
(2) ±1\pm 1
(3) −1-1
(4) 11
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Square the matrix and equate to OO.

This tests matrix multiplication and solving for a parameter.

Step 1. With A=[λ1−1−λ]A = \begin{bmatrix} \lambda & 1 \\ -1 & -\lambda \end{bmatrix}, compute A2A^2. Top-left: λ⋅λ+1⋅(−1)=λ2−1\lambda\cdot\lambda + 1\cdot(-1) = \lambda^2 - 1. Top-right: λ⋅1+1⋅(−λ)=0\lambda\cdot1 + 1\cdot(-\lambda) = 0. …

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