- Useful determinant facts for a 3×3 matrix
For a matrix of order 3:
- det(adj(M))=(detM)3−1=(detM)2
- det(kM)=k3det(M)
- det(M−1)=det(M)1
Given:
det(A)=3
We need to evaluate
det(adj(−4adj(−3adj(3adj((2A)−1)))))=2m3n
- Start from the innermost matrix
Let
M1=(2A)−1
Then
det(2A)=23det(A)=8⋅3=24
So
det(M1)=det((2A)−1)=241=2−33−1
- First adjugate
Let
M2=adj(M1)
Then
det(M2)=det(adj(M1))=(detM1)2=(241)2=2−63−2
Now multiply by 3:
M3=3M2
Hence
det(M3)=33det(M2)=27⋅2−63−2=2−631
- Second adjugate
Let
M4=adj(M3)
Then
det(M4)=(detM3)2=(2−631)2=2−1232
Now multiply by −3:
M5=−3M4
Since order is 3,
det(M5)=(−3)3det(M4)=−27⋅2−1232=−2−1235
- Third adjugate
Let
M6=adj(M5)
Then
det(M6)=(detM5)2=(−2−1235)2=2−24310
Now multiply by −4:
M7=−4M6
So
det(M7)=(−4)3det(M6)=−64⋅2−24310=−26⋅2−24310=−2−18310
- Final adjugate
Required matrix is
M8=adj(M7)
Therefore
det(M8)=(detM7)2=(−2−18310)2=2−36320
So,
2m3n=2−36320
which gives
m=−36,n=20
Hence
m+2n=−36+40=4
- Check with options
The value is
4
So the correct option is B.