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CBSE Class 12 Math 2009 Solved Paper

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Question : 5 of 29
Marks: +1, -0
If A is an invertible matrix of order 3 and |A| = 5, then find |adj. A|.
Solution:  
∣adjA∣=∣A∣n−1|adj A| = |A|^{n-1} , where n is order of square matrix
Given A is an invertible matrix of order 3
∣adjA∣=∣A∣3−1=∣A∣2|adj A| = |A|^{3-1} = |A|^2
Since, |A| = 5
∴ |adjA| = (5)( 5 ) = 25
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