If A = and B =
, verify that (AB)-1 = B-1 A-1.
Given:
To Verify: (AB)-1= B-1A-1
Firstly, we find the (AB)-1
Calculating AB
We have to find (AB)-1 and
Firstly, we find the adj AB and for that we have to find co-factors:
a11 (co – factor of -41) = (-1)1+1(26) = (-1)2(26) = 26
a12 (co – factor of 31) = (-1)1+2(-34) = (-1)3(-34) = 34
a21 (co – factor of -34) = (-1)2+1(31) = (-1)3(31) = -31
a22 (co – factor of 26) = (-1)2+2(-41) = (-1)4(-41) = -41
Now, adj AB = Transpose of co-factor Matrix
Calculating |AB|
= [-41 × 26 – (-34) × (31)]
= (-1066 + 1054)
= -12
Now, we have to find B-1A-1
Calculating B-1
Here,
We have to find A-1 and
Firstly, we find the adj B and for that we have to find co-factors:
a11 (co – factor of -4) = (-1)1+1(-4) = (-1)2(-4) = -4
a12 (co – factor of 3) = (-1)1+2(5) = (-1)3(5) = -5
a21 (co – factor of 5) = (-1)2+1(3) = (-1)3(3) = -3
a22 (co – factor of -4) = (-1)2+2(-4) = (-1)4(-4) = -4
Now, adj B = Transpose of co-factor Matrix
Calculating |B|
= [(-4) × (-4) – 3 × 5]
= (16 – 15)
= 1
Calculating A-1
Here,
We have to find A-1 and
Firstly, we find the adj A and for that we have to find co-factors:
a11 (co – factor of 9) = (-1)1+1(-2) = (-1)2(-2) = -2
a12 (co – factor of -1) = (-1)1+2(6) = (-1)3(6) = -6
a21 (co – factor of 6) = (-1)2+1(-1) = (-1)3(-1) = 1
a22 (co – factor of -2) = (-1)2+2(9) = (-1)4(9) = 9
Now, adj A = Transpose of co-factor Matrix
Calculating |A|
= [9 × (-2) – (-1) × 6]
= (-18 + 6)
= -12
Calculating B-1A-1
Here,
So,
So, we get
and
∴ (AB)-1 = B-1A-1
Hence verified