Matrices Question 4

Question 4 - 25 January - Shift 1

Let $x, y, z>1$ and

$ A= \begin{bmatrix} 1 & \log _{x} y & \log _{x} z \\ \log _{y} x & 2 & \log _{y} z \\ \log _{z} x & \log _{z} y & 3 \end{bmatrix} $

Then $|adj(adj A^{2})|$ is equal to

(1) $6^{4}$

(2) $2^{8}$

(3) $4^{8}$

(4) $2^{4}$

Show Answer

Answer: (2)

Solution:

Formula: Properties of Adjoint of a Matrix, Properties of Matrix Multiplication

$|A|=\frac{1}{\log x \cdot \log y \cdot \log z} \begin{vmatrix} \log x & \log y & \log z \\ \log x & 2 \log y & \log z \\ \log x & \log y & 3 \log z\end{vmatrix} =2$

$\Rightarrow|adj(adj A^{2})|=|A^{2}|^{4}=2^{8}$