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Putnam
1969 Putnam
B6
B6
Part of
1969 Putnam
Problems
(1)
Putnam 1969 B6
Source: Putnam 1969
3/31/2022
Let
A
A
A
and
B
B
B
be matrices of size
3
×
2
3\times 2
3
×
2
and
2
×
3
2\times 3
2
×
3
respectively. Suppose that
A
B
=
(
8
2
−
2
2
5
4
−
2
4
5
)
.
AB =\begin{pmatrix} 8 & 2 & -2\\ 2 & 5 &4 \\ -2 &4 &5 \end{pmatrix}.
A
B
=
8
2
−
2
2
5
4
−
2
4
5
.
Show that the product
B
A
BA
B
A
is equal to
(
9
0
0
9
)
.
\begin{pmatrix} 9 &0\\ 0 &9 \end{pmatrix}.
(
9
0
0
9
)
.
Putnam
matrix multiplication
matrix