Divisibility in the Integers. Intro to Analysis

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Homework Help Overview

The discussion revolves around proving the statement: If a|b and b|c, then a|c, within the context of integer divisibility in introductory analysis. Participants are exploring the implications of divisibility and the relationships between integers.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the definitions of divisibility and attempt to express relationships between the integers a, b, and c. Some participants consider substituting expressions for b and c based on their relationships with a, while others reflect on specific examples to clarify their understanding.

Discussion Status

The discussion is active, with participants sharing their thoughts and attempts at the proof. Some guidance has been offered, particularly in terms of substitution and the importance of integer relationships. There is an acknowledgment of the challenges involved in transitioning from computational to proof-based mathematics.

Contextual Notes

Participants note the constraints of their homework assignments, including a limited number of problems and the expectation to submit all problems for grading. This has led to a sense of pressure in mastering proof techniques.

Windowmaker
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Homework Statement




Prove: If a|b and b|c then a|c.

Assume a, b and c are integers.

Homework Equations



none

The Attempt at a Solution



If a divides b then that means that there is a

real integer "r" that is ra=b .

and since we assume b divides c then c=bs.

After here I got stuck. I was thinking maybe subsitute b and c for ar and bs, but it doesn't seem to get me anywhere. Thanks in advance.
 
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Windowmaker said:

Homework Statement




Prove: If a|b and b|c then a|c.

Assume a, b and c are integers.

Homework Equations



none

The Attempt at a Solution



If a divides b then that means that there is a

real integer "r" that is ra=b .

and since we assume b divides c then c=bs.

After here I got stuck. I was thinking maybe substitute b and c for ar and bs, but it doesn't seem to get me anywhere. Thanks in advance.
You have b in terms of a ? ...
 
Well I was thinking like we had 3|15. So a would be 3 and b would be 15. The r would be 5, so ra=b= 5*3=15. Or am I thinking about this wrong?
 
If a|b, then there exists an int r such that a*r = b.

If b|c, then there exists an int s such that s*b = c.

Since b = a*r, we have s*(a*r)=a*(r*s) = c.

Since r*s is an integer, this shows that c equals a multiplied by an integer, meaning a|c.
 
Windowmaker said:
Well I was thinking like we had 3|15. So a would be 3 and b would be 15. The r would be 5, so ra=b= 5*3=15. Or am I thinking about this wrong?
If this is a concrete example, you'll need another number.

You have 3|15, that's like a|b. Now you need b|c, so in the example, 15| ? .
 
Oh my goodness...First class on proofs its just simple subistution. Thanks man, cleared up a lot!
 
Windowmaker said:
Oh my goodness...First class on proofs its just simple substitution. Thanks man, cleared up a lot!
Well, I saw that you were almost there in your original post. I'd rather lead you to discover what's missing than to simply provide the bridge.

Good luck with the proofs. It can be challenging, coming up with some of them, but very rewarding once you do !
 
What sucks about this course is there's only like 10 problems per section. He collects all 10 or so problems, so there's no extra problems to work out. Its not overly difficult, its just a bit different than the math I am used too. Computational math is much different than proof based math. Lol.
 

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