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Let A=[1−23121λ2−3]A = \begin{bmatrix} 1 & -2 & 3 \\ 1 & 2 & 1 \\ \lambda & 2 & -3 \end{bmatrix}. If A−1A^{-1} does not exist, then λ=\lambda =

Solution

✅ Correct Option: 4

A−1A^{-1} does not exist when ∣A∣=0|A| = 0. Expanding: ∣A∣=1(−6−2)+2(−3−λ)+3(2−2λ)=−8−6−2λ+6−6λ=−8−8λ|A| = 1(-6-2) + 2(-3-\lambda) + 3(2-2\lambda) = -8 - 6 - 2\lambda + 6 - 6\lambda = -8 - 8\lambda. Setting to zero gives λ=−1\lambda = -1.

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