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irrational (Definition)

An irrational number is a real number which cannot be represented as a ratio of two integers. That is, if $x$ is irrational, then

$$ x \ne \frac{a}{b} $$

with $a,b \in \mathbb{Z}$ and $b \ne 0$

Examples

  1. $\sqrt[p]{2}$ is irrational for $p=2,3,\ldots$
  2. $\pi, e$ and $\sqrt[p]{2}$ for $p=2,3,\ldots$ are irrational,
  3. It is not known whether Euler's constant is rational or irrational.

Properties

  1. It $a$ is a real number and $a^n$ is irrational for some $n=2,3,\ldots$ then $a$ is irrational (proof).
  2. The sum, difference, product, and quotient (when defined) of two numbers, one rational and another irrational, is irrational. (proof).




"irrational" is owned by yark. [ full author list (3) | owner history (1) ]
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See Also: transcendental number, algebraic number, integer, Lindemann-Weierstrass theorem, Gelfond's theorem, proof that the rationals are countable

Other names:  irrational number

Attachments:
$\sqrt[n]{2}$ is irrational for $n\ge 3$ (proof using Fermat's last theorem) (Proof) by matte
irrational to an irrational power can be rational (Result) by Koro
if $a^n$ is irrational then ${a}$ is irrational (Theorem) by Wkbj79
rational and irrational (Result) by pahio
rational Briggsian logarithms of integers (Theorem) by pahio
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Cross-references: numbers, quotient, product, difference, sum, rational, Euler's constant, integers, ratio, real number
There are 92 references to this entry.

This is version 7 of irrational, born on 2001-11-04, modified 2008-11-09.
Object id is 661, canonical name is Irrational.
Accessed 19647 times total.

Classification:
AMS MSC11J72 (Number theory :: Diophantine approximation, transcendental number theory :: Irrationality; linear independence over a field)
 11J82 (Number theory :: Diophantine approximation, transcendental number theory :: Measures of irrationality and of transcendence)

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