If a divides bc, then a divides b or a divides c

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Homework Help Overview

The discussion revolves around the divisibility property in number theory, specifically the statement "If a divides bc, then a divides b or a divides c." Participants are examining the validity of this statement through examples and reasoning.

Discussion Character

  • Conceptual clarification, Assumption checking, Mixed

Approaches and Questions Raised

  • Some participants attempt to prove the statement using algebraic manipulation, while others question the validity of the proof by providing counterexamples. There is also a focus on the implications of dividing by a variable that could be zero.

Discussion Status

The discussion is active, with participants presenting differing viewpoints on the original statement. Some have provided counterexamples that challenge the assertion, while others are critiquing the methods used in the proofs. There is no explicit consensus, but the dialogue is exploring various interpretations and assumptions.

Contextual Notes

Participants are considering the implications of specific values for b and c, including the case where b could be zero, which raises questions about the validity of division in the proofs presented. There is also mention of the context of introductory number theory, suggesting a foundational level of understanding among participants.

Dustinsfl
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If a|bc, then a|b or a|c.

a|bc\Leftrightarrow am=bc\Leftrightarrow a\left(\frac{m}{b}\right)=c

Hence, a|c
 
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Dustinsfl said:
If a|bc, then a|b or a|c.

a|bc\Leftrightarrow am=bc\Leftrightarrow a\left(\frac{m}{b}\right)=c

Hence, a|c

That statement is false as stated. Let b = 6, c = 10. Then a = 4 divides bc = 60 but a doesn't divide either b or c.
 
Your proof is false because you are dividing by b. This is incorrect since b could be 0.
 
Last edited:
ocohen said:
This is only true if b or c is prime. As a side note, your proof is false because you are dividing by b. This is incorrect since b could be 0.

he also doesn't know whether m/b will be an integer or not.

I am guessing you are reading an introductory number theory book. you should refrain from dividing as much as possible in your proofs. modding out is acceptable later when you start doing it, but don't divide unless you know that the denominator is NOT zero and the quotient is an integer.
 

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