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Mathematics
Mathematics
Problem
Explain why
I
3
B
=
B
I_3 B = B
I
3
B
=
B
for every
3
×
p
3 \times p
3
×
p
matrix
B
B
B
, but the product
B
I
3
B I_3
B
I
3
is defined only when
B
B
B
has exactly 3 columns.
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