If it is a fraction, then we should be able to create it dvery own as a simplified fractivity favor this:


(m and also n are both totality numbers)

And we are hoping that as soon as we square it we acquire 2:

(m/n)2 = 2

which is the very same as

m2/n2 = 2

or put one more method, m2 is twice as substantial as n2:

m2 = 2 × n2

Have a Try Yourself

See if you have the right to find a worth for m and n that works!

Example: let us attempt m=17 and also n=12:

m/n = 17/12

When we square that we get

172/122 = 289/144 = 2.0069444...

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Which is close to 2, yet not rather right

You deserve to view we really want m2 to be twice n2 (289 is about twice 144). Can you do better?

Even and Odd

Now, let us take up this concept that m2 = 2 × n2

It actually suggests that m2 must be an even number.

Why? Due to the fact that whenever we multiply by an also number (2 in this case) the outcome is an even number. Like this:

Operation Result Example
Even × Even Even 2 × 8 = 16
Even × Odd Even 2 × 7 = 14
Odd × Even Even 5 × 8 = 40
Odd × Odd Odd 5 × 7 = 35

And if m2 is even, then m should be even (if m was odd then m2 is additionally odd). So:

m is even

And all also numbers are a multiple of 2, so m is a multiple of 2, so m2 is a multiple of 4.

And if m2 is a multiple of 4, then n2 must be a multiple of 2 (remembering that m2/n2 = 2).

And so ...

n is additionally even

But hang on ... if both m and n are even, we have to have the ability to simplify the fractivity m/n.

But we already sassist that it was simplified ...


... and if it isn"t already streamlined, then let us simplify it now and start again. But that still gets the very same result: both n and m are even.

Well, this is silly - we can display that both n and m are constantly even, no matter that we have streamlined the fraction already.

So somepoint is terribly wrong ... it have to be our initially assumption that the square root of 2 is a fraction. It can"t be.

And so the square root of 2 cannot be composed as a fraction.


We speak to such numbers "irrational", not bereason they are crazy but bereason they cannot be created as a ratio (or fraction). And we say:

"The square root of 2 is irrational"

It is thmust be the initially irrational number ever uncovered. But tbelow are lots even more.

Reductio ad absurdum

By the way, the method we supplied to prove this (by initially making an assumption and also then seeing if it works out nicely) is called "proof by contradiction" or "reductio ad absurdum".

Reduction ad absurdum: a type of logical debate wright here one assumes a insurance claim for the sake of debate and also derives an absurd or ridiculous outcome, and also then concludes that the original case have to have actually been wrong as it resulted in an absurd outcome. (from Wikipedia)


Many kind of years ago (roughly 500 BC) Greek mathematicians like Pythagoras thought that all numbers can be shown as fractions.

And they thought the number line was made up completely of fractions, bereason for any two fractions we deserve to always uncover a fraction in in between them (so we have the right to look closer and also closer at the number line and uncover even more and more fractions).

Example: in between 1/4 and 1/2 is 1/3. Between 1/3 and also 1/2 is 2/5, between 1/3 and also 2/5 is 3/8, and also so on.

(Note: The basic method to find a portion in between two various other fractions is to add the tops and add the bottoms, so between 3/8 and 2/5 is (3+2)/(8+5) = 5/13).

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So because this procedure has actually no finish, there are infinitely many such points. And that appears to fill up the number line, doesn"t it?

And they were incredibly happy via that ... until they discovered that the square root of 2 was not a fraction, and also they had to re-think their principles completely!


The square root of 2 is "irrational" (cannot be written as a fraction) ... bereason if it could be composed as a portion then we would certainly have actually the absurd situation that the fraction would certainly have actually also numbers at both top and also bottom and so might always be simplified.