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

In summary, the conversation discusses whether the statement "AB = AC implies B=C" holds true for matrices. The hypothesis is that AB=AC while A is not a zero matrix, and the thesis is that B=C. The attempt at a solution shows a property of matrices being used to solve the problem, but the conclusion is questioned as there are matrices where AB=0 and neither A nor B are zero. The mistake is identified as the assumption that A(B-C)=0 implies A=0 or (B-C)=0, which is not always true for matrices.
  • #1
Brutus
7
0

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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  • #2
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.
 
  • #3
ok, thanks
 

1. What is the purpose of a proof in matrix algebra?

A proof in matrix algebra is used to demonstrate the validity of a mathematical proposition or statement. It is a way to logically and systematically show that a given statement is true.

2. What are some common mistakes in a proof of a matrix algebra proposition?

Some common mistakes in a proof of a matrix algebra proposition include incorrect use of matrix operations, incorrect application of mathematical principles, and errors in notation or algebraic manipulation.

3. How can I check my proof for mistakes?

One way to check for mistakes in a proof is to carefully review each step and make sure it follows logically from the previous step. It can also be helpful to have someone else review your proof and provide feedback or to use a proof-writing tool or software to check for errors.

4. What should I do if I find a mistake in my proof?

If you find a mistake in your proof, it is important to carefully analyze the mistake and understand why it occurred. Then, you can correct the mistake and rework the proof to ensure its accuracy. If you are unsure how to correct the mistake, seek assistance from a colleague or mentor.

5. Are there any tips for avoiding mistakes in a proof of a matrix algebra proposition?

Yes, there are several tips for avoiding mistakes in a proof of a matrix algebra proposition. These include carefully checking all calculations and equations, using proper notation and terminology, and being thorough and precise in your explanations. It can also be helpful to double-check all steps and to seek feedback from others before finalizing your proof.

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