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If A = 2 1 1 2 ⎡ ⎤ ⎢ ⎥ − ⎢ ⎥ ⎣ ⎦ , B = 1 0 1 1 ⎡ ⎤ ⎢ ⎥ ⎣ ⎦ , C = ABA T and X = A T C 2 A, then det X is equal to :

1. 243
2. 891
3. 729
4. 27

Correct answer: 729

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