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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

The inverse fails to exist exactly when ∣A∣=0|A| = 0. Expanding along the first row, ∣A∣=(−8)+2(−3−λ)+3(2−2λ)=−8−8λ|A| = (-8) + 2(-3-\lambda) + 3(2-2\lambda) = -8-8\lambda. Setting this to zero gives λ=−1\lambda = -1.

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