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Mathematics
Problem
For the matrix
A
=
(
1
2
3
0
1
4
5
6
0
)
A = \begin{pmatrix} 1 & 2 & 3 \\ 0 & 1 & 4 \\ 5 & 6 & 0 \end{pmatrix}
A
=
1
0
5
2
1
6
3
4
0
, what is the entry in the second row and first column of
A
−
1
A^{-1}
A
−
1
? a)
18
18
18
b)
20
20
20
c)
−
20
-20
−
20
d)
−
18
-18
−
18
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