If a matrix A has inverses B and C, then which one of the following is correct ?
A
B may not be equal to C
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B
B should be equal to C.
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C
B and C should be unit matrices
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D
None of the above
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Solution
The correct option is D B should be equal to C. The matrix A cannot have two inverse. Suppose BA=I and AC=I then B=C. According to this proof by parentheses:
B(AC)=(BA)C
This implies BI=IC
Therefore B=C
This shows that a left-inverse B (multiplying from the left) and a right-inverse C (multiplying A from the right to give AC=I) must be the same matrix.