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If P=[1x3133244]P = \begin{bmatrix} 1 & x & 3 \\ 1 & 3 & 3 \\ 2 & 4 & 4 \end{bmatrix} is the adjoint of 3x3 matrix A and ∣A∣|A| is 4, then xx is equal to :

Solution

✅ Correct Option: 3

Since P=adj(A)P=\text{adj}(A) for a 3×33\times3 matrix, ∣P∣=∣A∣n−1=42=16|P|=|A|^{n-1}=4^2=16.

Expanding ∣P∣|P|: 1(12−12)−x(4−6)+3(4−6)=0+2x−6=2x−61(12-12)-x(4-6)+3(4-6)=0+2x-6=2x-6.

Setting 2x−6=162x-6=16 gives x=11x=11.

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