Question about irrational numbers

In summary, the conversation discusses the proof that \sqrt{p/q} is an irrational number, where p and q are distinct primes. The proof is based on the assumption that \sqrt{p/q} can be written as a rational number, which leads to a contradiction. The proof also takes into account the fact that GCD (a,b) must equal 1 in order for the assumption to hold true.
  • #1
olcyr
5
0
Let p and q be distinct primes. Prove that [tex]\sqrt{p/q}[/tex] is a irrational number.
 
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  • #2
olcyr said:
Let p and q be distinct primes. Prove that [tex]\sqrt{p/q}[/tex] is a irrational number.

It isn't a homework. I just need to prove it!

Thank you,
Olcyr.
 
  • #3
It's quite easy. Assume, that [tex] \sqrt{p/q}=a/b[/tex], where a and b are relative primes, ie GCD (a,b)=1.

This is equivalent to [tex]pb^2=qa^2[/tex]. Since p and q are distinct primes, p | a^2 => p | a => The right side is divisible by p^2, and this is a contradiction, because the left side is not (because b is not divisible by p, since GCD (a,b)=1)
 
  • #4
I din't understand why b isn't divisible by p.

Thank you for your answer!
 
  • #5
because if b is divisible by p, than GCD (a,b) is at least p, but we assumed that it equals to 1
 
  • #6
Thanks! :)
 

Related to Question about irrational numbers

What are irrational numbers?

Irrational numbers are numbers that cannot be expressed as a ratio of two integers. They are decimal numbers that do not terminate or repeat, such as pi (3.141592...) or the square root of 2 (1.414213...).

How can you tell if a number is irrational?

If a number cannot be written as a fraction with integers in the numerator and denominator, then it is irrational. Another way to identify irrational numbers is by finding their decimal representations, which will never terminate or repeat.

What is the difference between irrational and rational numbers?

Rational numbers can be expressed as a ratio of two integers, while irrational numbers cannot. Rational numbers also have decimal representations that either terminate or repeat, while irrational numbers have decimal representations that never terminate or repeat.

Can irrational numbers be negative?

Yes, irrational numbers can be both positive and negative. Examples of negative irrational numbers include -pi, -sqrt(2), and -e (2.718281...).

Why are irrational numbers important?

Irrational numbers play an important role in mathematics and science. They are used to solve problems in geometry, to describe the behavior of waves, and to calculate probabilities in statistics. They are also used in many real-life applications, such as engineering and finance.

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