Proof: integers divisibility property

In summary, the statement "If a divides b but not c, then a does not divide b + c" is true, but the converse "If a does not divide b + c, then a divides b but not c" is false. This can be proven using a proof by contradiction method and finding a counterexample for the converse statement.
  • #1
Prathep
7
0
Someone please help me with this qiestion:

Prove that for all integers a, b, and c, if a divides b but not c then a does not
divide b + c, but the converse is false.

Thanks.
 
Last edited:
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  • #2
Looks like a homework problem to me! First write out the definitions: If "a divides b" then b= an for some integer n. I would use "proof by contradiction". Suppose you know that a divides b+c, that is, that b+c= am for some integer m and that b= an for some integer n. Can you use that to contradict "a does not divide c"?

The "converse" of that statement is, of course, "if a does not divide b+ c, then a divides b but not c". It should be fairly simple to find a counter example for that, or the more general "converse", "if a does not divide b+ c, then it must divide one but not the other".
 
  • #3
I imagine the question does refer to the more general converse. The specific converse can be disproved simply by symmetry arguments, without using a shred of number theory.
 

1. What is the divisibility property of integers?

The divisibility property of integers states that if one integer is evenly divisible by another integer, the remainder is equal to 0. In other words, when one integer is divided by another, the result is a whole number with no remainder.

2. How can the divisibility property be proven?

The divisibility property can be proven using mathematical induction. This involves showing that the property holds for the first few integers, and then assuming that it holds for a particular integer, and proving that it also holds for the next consecutive integer. By repeating this process, the property can be shown to hold for all integers.

3. What is the relationship between the divisibility property and prime numbers?

The divisibility property is closely related to prime numbers. A prime number is a positive integer that is only divisible by 1 and itself. This means that if a number is not divisible by any smaller integers, then it must be a prime number. Therefore, the divisibility property can be used to determine if a number is prime or not.

4. Are there any exceptions to the divisibility property?

Yes, there are a few exceptions to the divisibility property. One exception is when dividing by 0, as this is undefined. Another exception is when dividing by a fraction, as the result may not be a whole number. Additionally, when dividing by a negative number, the remainder may be negative instead of 0.

5. How is the divisibility property used in everyday life?

The divisibility property is commonly used in everyday life, especially in fields such as finance, cryptography, and computer science. For example, banks use the divisibility property to ensure that transactions are accurate and to prevent fraud. Cryptographers use this property to create secure encryption algorithms. In computer science, the divisibility property is used in programming to check for errors and validate data.

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