Prove by Induction: 3n-1 is Divisible by 2

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Discussion Overview

The discussion revolves around proving by induction that the expression 3n-1 is divisible by 2. Participants are exploring the steps involved in the induction process, including the formulation of the induction hypothesis and the substitution needed for the proof.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant expresses uncertainty about how to approach the proof by induction for the statement that 3n-1 is divisible by 2.
  • Another participant suggests using the induction hypothesis 3^n = 2a + 1 for some integer a and proposes substituting this into the expression for 3^{n+1}-1.
  • A follow-up question seeks clarification on the substitution process mentioned.
  • Substitution is clarified with the expression 3^{n+1}-1 = 3.3^n-1 = 3.(2a+1)-1, leading to the conclusion that the resulting expression is 6a + 2, which can be factored to show it is divisible by 2.

Areas of Agreement / Disagreement

Participants are working collaboratively on the proof, but there is no explicit consensus on the overall approach or final conclusion, as the discussion is still in progress.

Contextual Notes

Some steps in the mathematical reasoning are not fully detailed, and assumptions regarding the induction hypothesis may need further clarification.

BloodyFrozen
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I was doing this for practice and came across this problem-- I have no clue how to prove it.

By Induction, prove that 3n-1 is divisible by 2.

1) 3-1=2, divisible by two; good so far

Now I have no clue how to approach this.:bugeye:

Please help. Thanks in advance:smile:
 
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Hi BloodyFrozen! :smile:

So, the induction hypothesis says that

[tex]3^n=2a+1[/tex]

for some a. Now, try substitute this in [itex]3^{n+1}-1[/itex].
 
micromass said:
Hi BloodyFrozen! :smile:

So, the induction hypothesis says that

[tex]3^n=2a+1[/tex]

for some a. Now, try substitute this in [itex]3^{n+1}-1[/itex].


What do you mean sustituting it in?
 
BloodyFrozen said:
What do you mean sustituting it in?

[tex]3^{n+1}-1=3.3^n-1=3.(2a+1)-1[/tex]
 
micromass said:
[tex]3^{n+1}-1=3.3^n-1=3.(2a+1)-1[/tex]

Ok.
6a+2=2(3a+1).

Since this is multiplied by 2, it must be divisible by 2.
Thanks again (if you know what I mean ;P) micromass!
 

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