- A32
- B81
- C64
- D108
View written solutionFree
Correct answer: C
-
We need to find for matrices with
-
Use the determinant property for a product: So, \begin{align*} &\left|A^T A,(\operatorname{adj}(2A))^{-1}(\operatorname{adj}(4B))(\operatorname{adj}(AB))^{-1}AA^T\right| \ &=|A^TA|\cdot |(\operatorname{adj}(2A))^{-1}|\cdot |\operatorname{adj}(4B)|\cdot |(\operatorname{adj}(AB))^{-1}|\cdot |AA^T|. \end{align*}
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Compute the easy determinants first.
For any square matrix , Hence, and similarly,
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Use the adjoint determinant formula. For an matrix , Here , so Therefore,
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Compute each remaining factor.
(i)
Since is , Thus, so
(ii)
Hence,
(iii)
First, So, and therefore,
- Multiply all factors: \begin{align*} \text{Required determinant} &=9\cdot \frac{1}{24^2}\cdot 128^2\cdot \frac{1}{36}\cdot 9. \end{align*}
Now simplify: so
Since we get
But a cleaner simplification is: Thus, \begin{align*} \text{Required determinant} &=9\cdot \frac{256}{9}\cdot \frac{1}{36}\cdot 9 \ &=256\cdot \frac{9}{36} \ &=256\cdot \frac{1}{4} \ &=64. \end{align*}
- Therefore the correct option is So, Option C is correct.
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