Need help to find my mistake in a simple proof of a matrix algebra proposition.

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SUMMARY

The discussion centers on the proof of a matrix algebra proposition where the hypothesis states that if \( AB = AC \) and \( A \neq 0 \), then it is concluded that \( B = C \). The user identifies a flaw in their reasoning, recognizing that the property \( A(B-C) = 0 \) does not imply \( B = C \) when \( A \) is a non-zero matrix. This is due to the existence of non-zero matrices \( A \) and \( B \) such that \( AB = 0 \), demonstrating that the conclusion does not hold universally.

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Brutus
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Homework Statement


Is the following true for matrices?

Hypotesis:
AB = AC
A != 0(zero matrix)

Thesis:
B=C

The Attempt at a Solution



AB = AC
AB - AC = 0(zero matrix)
AB - AC = A(B-C) // using the following property: A(B+C) = AB + AC iff A is mn matrix and BC are np matrices
A(B-C) = 0 <=> B=C because A != 0
QED

There is something wrong because there are matrices where AB = AC and B != C.
Where is my mistake?
 
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There are matrices where AB=0 and neither A nor B are zero. You can't say A(B-C)=0 implies A=0 or (B-C)=0 like you can with real numbers.
 
ok, thanks
 

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