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

• BloodyFrozen
In summary, The conversation discusses how to prove that 3n-1 is divisible by 2 using induction. The participants go through the steps of the proof, including substituting in the induction hypothesis and showing that the result is divisible by 2.
BloodyFrozen
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.

Hi BloodyFrozen!

So, the induction hypothesis says that

$$3^n=2a+1$$

for some a. Now, try substitute this in $3^{n+1}-1$.

micromass said:
Hi BloodyFrozen!

So, the induction hypothesis says that

$$3^n=2a+1$$

for some a. Now, try substitute this in $3^{n+1}-1$.

What do you mean sustituting it in?

BloodyFrozen said:
What do you mean sustituting it in?

$$3^{n+1}-1=3.3^n-1=3.(2a+1)-1$$

micromass said:
$$3^{n+1}-1=3.3^n-1=3.(2a+1)-1$$

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!

## 1. What is the principle of mathematical induction?

The principle of mathematical induction is a powerful method for proving statements about natural numbers. It states that if a statement is true for a base case (usually n = 1) and if it can be proven that if the statement is true for some number n, then it must also be true for n+1, then the statement is true for all natural numbers.

## 2. How do you use mathematical induction to prove that 3n-1 is divisible by 2?

To prove that 3n-1 is divisible by 2 for all natural numbers, we must first show that it is true for the base case n=1. We can see that 3(1)-1 = 2, which is divisible by 2. Next, we assume that the statement is true for some arbitrary natural number k. This means that 3k-1 is divisible by 2. We can then use this assumption to show that the statement is also true for k+1. By substituting k+1 for n in the original statement, we get 3(k+1)-1 = 3k+2, which is also divisible by 2. This proves that the statement is true for all natural numbers.

## 3. Can you provide a specific example to demonstrate the proof by induction for 3n-1?

Sure. Let's use n=3 as an example. We can see that 3(3)-1 = 8, which is divisible by 2. Next, we assume that the statement is true for some arbitrary natural number k. This means that 3k-1 is divisible by 2. By substituting k+1 for n in the original statement, we get 3(k+1)-1 = 3k+2, which is also divisible by 2. This proves that the statement is true for n=3 and all natural numbers.

## 4. Why is it important to prove that 3n-1 is divisible by 2?

Proving that 3n-1 is divisible by 2 is important because it is a fundamental property of natural numbers. It helps us to understand the relationships and patterns between numbers, and it can be used to prove other mathematical statements and formulas. It also has practical applications, such as in computer science and cryptography.

## 5. Are there any tips for successfully using induction to prove statements?

Yes, there are a few tips that can help make the process of using induction to prove statements easier. First, make sure to clearly state the statement you are trying to prove and the base case. Next, use precise mathematical language and notation. It can also be helpful to work through some specific examples to better understand the pattern and logic behind the proof. Finally, don't be afraid to seek help or clarification if you are struggling with the proof.

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