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If A=[4−1λ2061−27]A = \begin{bmatrix} 4 & -1 & \lambda \\ 2 & 0 & 6 \\ 1 & -2 & 7 \end{bmatrix}, then 12A−1\frac{1}{2}A^{-1} exist if

Solution

✅ Correct Option: 3

12A−1\frac12 A^{-1} exists exactly when A−1A^{-1} exists, i.e. ∣A∣≠0|A|\neq 0. Expanding, ∣A∣=4(0+12)+1(14−6)+λ(−4−0)=56−4λ|A|=4(0+12)+1(14-6)+\lambda(-4-0)=56-4\lambda. So 56−4λ≠056-4\lambda\neq 0 gives λ≠14\lambda\neq 14.

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