Proof that Log2 of 5 is irrational

In summary, the conversation discusses proving that log2 of 5 is irrational and the attempt at a solution involves using unique factorization to show that both a and b must be even, which contradicts the initial assumption that a/b is a rational number. The concept of unique factorization is also brought up.
  • #1
Pascal's Pal
9
0

Homework Statement



Prove that log2 of 5 is irrational.

Homework Equations



None.

The Attempt at a Solution



I just had a glimpse of the actual solution, but I'm wondering if mine would work too.

2^(a/b) = 5

square both sides...

2^(2a/b) =25

2 = 25^(b/2a)

(b/2a) = log25 of 2

b = 2aLog25 of 2

b is even...

and through a similar process...by taking the square root of both sides of "2^(a/b) = 5" you can arrive at a being even too. So how can they both be even etc etc.
 
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  • #2
[tex]\log_2 5 = a/b[/tex] so [tex]2^{a/b} = 5 \implies 2^a = 5^b[/tex]. Now use unique factorization.
 
  • #3
Kummer said:
[tex]\log_2 5 = a/b[/tex] so [tex]2^{a/b} = 5 \implies 2^a = 5^b[/tex]. Now use unique factorization.

But does mine work?
 
  • #4
Kummer said:
[tex]\log_2 5 = a/b[/tex] so [tex]2^{a/b} = 5 \implies 2^a = 5^b[/tex]. Now use unique factorization.

What is unique factorization ?
 

What is the proof that Log2 of 5 is irrational?

The proof involves using a proof by contradiction method. Assume that Log2 of 5 is rational and can be expressed as a fraction of two integers. Then use the properties of logarithms to show that this leads to a contradiction.

Why is it important to prove that Log2 of 5 is irrational?

Proving that Log2 of 5 is irrational is important because it helps to establish the irrationality of the number 2, which is a fundamental number in mathematics. It also helps to show that not all numbers can be expressed as fractions, which expands our understanding of numbers and their properties.

Can the proof that Log2 of 5 is irrational be generalized to other logarithms?

Yes, the same proof by contradiction method can be used to show that Logb of a is irrational for any base b and positive integer a that is not a perfect power of b. This is known as the Gelfond-Schneider theorem.

What are the practical applications of proving that Log2 of 5 is irrational?

While the proof itself may not have direct practical applications, the concept of irrational numbers is used extensively in various fields of mathematics, science, and engineering. Understanding the irrationality of Log2 of 5 helps to build a strong foundation for more complex mathematical concepts.

Are there other proofs for the irrationality of Log2 of 5?

Yes, there are other proofs for the irrationality of Log2 of 5, such as using continued fractions or the prime factorization of numbers. However, the proof by contradiction method is the most commonly used and easiest to understand.

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