A=l 2 7 45 4 5 27 1 3 20 . Find the third column of A1 ( subscript -1) without c
ID: 3136627 • Letter: A
Question
A=l
2 7 45
4 5 27
1 3 20
.
Find the third column of
A1 ( subscript -1)
without computing the other two columns.
How can the third column of
A1 ( subscript -1)
be found without computing the other columns?
A.
Row reduce the augmented matrix [AI3( not 13 but capital I subscript 3].
B.
Row reduce the augmented matrix [A e3],where e3 is the third column of I3.( capital I subscript 3)
C.
Row reduce the augmented matrix
A
e3
,
where e3
is the third row of I3.( capital I subscript 3- not 13)
D.
Solve the equation
Ae3=b
for
e3,
where
e3
is the third column of I3( capital I subscript 3, not 13)
and b is the third column of
A1( A subscript -1 not A subtract 1).
The third column of
A1 ( A subscript -1)
is __________________
(Type an integer or decimal for each matrix element.)
Explanation / Answer
In order to compute the third column of A-1, we have to solve the equation AX = (0 0 1)T, where (0,0,1)T is the third column of I3. Let B = [A|(0,0,1)T]=
-2
-7
-45
0
4
5
27
0
1
3
20
1
To solve equation AX = (0 0 1)T , we can row reduce B as under:
Multiply the 1st row by -1/2
Add -4 times the 1st row to the 2nd row
Add -1 times the 1st row to the 3rd row
Multiply the 2nd row by -1/9
Add 1/2 times the 2nd row to the 3rd row
Add -7 times the 3rd row to the 2nd row
Add -45/2 times the 3rd row to the 1st row
Add -7/2 times the 2nd row to the 1st row
Then the RREF of B is
1
0
0
2
0
1
0
-7
0
0
1
1
Then the 3rd column of A-1 is (2,-7,1)T.
-2
-7
-45
0
4
5
27
0
1
3
20
1