Let A= bmatrix1 & 1 & 2\ -2 & 0 & 1\ 1 & 3 & 5 bmatrix. Then the sum of all elements of the matrix adj (adj (2(adj A)-1 ) ) is equal to:
- 3
- 4
- -4
- -3
Answer
(4) -3
Solution
|A|=1(0-3)-1(-10-1)+2(-6-0)=-3+11-12=-4
adj A=|A|A-1 (adj A)-1= A|A|=- A4
Let B=2(adj A)-1=- A2
|B|= (- 12 )3|A|=- 18(-4)= 12
For a 3 3 matrix, adj(adj B)=|B|3-2B=|B| B
adj(adj B)= 12 (- A2 )=- A4
Sum of elements of A=1+1+2-2+0+1+1+3+5=12
Required sum =- 124=-3
Answer: (4)