Discrete math - proof of divisibility question

Click For Summary
SUMMARY

The statement "If a|b and a|c, then one (or both) of b|c or c|b holds" is false. A counter-example is provided with a = 5, b = 10, and c = 15, demonstrating that neither 10 divides 15 nor 15 divides 10. This disproves the original claim effectively by showing that the divisibility relationship does not necessarily hold in all cases.

PREREQUISITES
  • Understanding of divisibility notation (a|b)
  • Basic knowledge of discrete mathematics
  • Familiarity with constructing mathematical proofs
  • Ability to create counter-examples in mathematical arguments
NEXT STEPS
  • Study the properties of divisibility in number theory
  • Learn about constructing and analyzing mathematical proofs
  • Explore counter-examples in mathematical logic
  • Investigate related concepts such as greatest common divisors and least common multiples
USEFUL FOR

Students of discrete mathematics, educators teaching number theory, and anyone interested in mathematical proofs and logic.

dgamma3
Messages
12
Reaction score
0
is this true or false:

If a|b and a|c, then one (or both) of b|c or c|b holds.

if I want to disprove this, can I:

let a = 5, x = 2 and y = 3.

b=ax
c=ay

then c=bz
and c = bg doesn't hold.
 
Physics news on Phys.org
Why make it so complicated? You constructed a counter-example:

a=5 , b=10 c=15 , and neither 10|15 nor 15|10.
 

Similar threads

Replies
23
Views
4K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 2 ·
Replies
2
Views
1K
Replies
4
Views
2K
Replies
3
Views
4K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 1 ·
Replies
1
Views
2K
Replies
3
Views
2K
  • · Replies 14 ·
Replies
14
Views
2K