Question:medium

If $A$ is a non-singular square matrix of order 3 and $|A^{-1}| = 24$, then the value of $|2A(\operatorname{adj}(3A))|$ is:

Show Hint

Use determinant properties for scalar multiplication and the formula \(|\operatorname{adj}(A)| = |\det(A)|^{n-1}\).
Updated On: Apr 2, 2026
  • \(\frac{1}{64}\)
  • \(\frac{9}{192}\)
  • \(\frac{27}{64}\)
  • \(\frac{9}{64}\)
Show Solution

The Correct Option is D

Solution and Explanation

Given a non-singular 3x3 matrix \( A \) with \( |A^{-1}| = 24 \). Since \( |A| = \frac{1}{|A^{-1}|} \), we have \( |A| = \frac{1}{24} \).

We aim to compute \( |2A(\operatorname{adj}(3A))| \). Using the property \( \operatorname{adj}(B) = |B|B^{-1} \), we get \( \operatorname{adj}(3A) = |3A|(3A)^{-1} \).

First, calculate \( |3A| \). For a 3x3 matrix, \( |3A| = 3^3|A| = 27|A| \).

Substituting \( |A| = \frac{1}{24} \), we find \( |3A| = 27 \times \frac{1}{24} = \frac{27}{24} \).

Substituting this into the expression for \( \operatorname{adj}(3A) \):

\(\operatorname{adj}(3A) = \frac{27}{24}(3A)^{-1} \).

Now, we evaluate the target determinant:

\(|2A(\operatorname{adj}(3A))| = |2A| \cdot |\operatorname{adj}(3A)| = |2A| \cdot \left|\frac{27}{24}(3A)^{-1}\right| \).

Calculate \( |2A| \):

\(|2A| = 2^3|A| = 8|A| = 8 \times \frac{1}{24} = \frac{8}{24} = \frac{1}{3} \).

Calculate \( \left|\frac{27}{24}(3A)^{-1}\right| \):

\( \left|\frac{27}{24}(3A)^{-1}\right| = \frac{27}{24}\left|(3A)^{-1}\right| = \frac{27}{24} \times \frac{1}{|3A|} = \frac{27}{24} \times \frac{1}{\frac{27}{24}} = \frac{27}{24} \times \frac{24}{27} = 1 \).

Therefore, the final result is:

\(|2A(\operatorname{adj}(3A))| = \frac{1}{3} \times 1 = \frac{1}{3} \).

The value is \(\frac{1}{3}\).

Was this answer helpful?
0