Definition:Power (Algebra)/Integer

From ProofWiki
Jump to navigation Jump to search


This article is complete as far as it goes, but it could do with expansion.
In particular: Add a second definition for $x^n$ for $n < 0$: $x^n = \dfrac 1 {x^{-n} }$
You can help $\mathsf{Pr} \infty \mathsf{fWiki}$ by adding this information.
To discuss this page in more detail, feel free to use the talk page.
When this work has been completed, you may remove this instance of {{Expand}} from the code.
If you would welcome a second opinion as to whether your work is correct, add a call to {{Proofread}} the page.


Definition

Let $x \in \R$ be a real number.

Let $n \in \Z$ be an integer.

The expression $x^n$ is called $x$ to the power of $n$.

$x^n$ is defined recursively as:


$x^n = \begin {cases} 1 & : n = 0 \\ & \\ x \times x^{n - 1} & : n > 0 \\ & \\ \dfrac {x^{n + 1} } x & : n < 0 \end {cases}$

where $\dfrac {x^{n + 1} } x$ denotes division.


Even Power

Let $x \in \R$ be a real number.

Let $n \in \Z$ be an even integer.


Then $x^n$ is called an even power of $x$.


Odd Power

Let $x \in \R$ be a real number.

Let $n \in \Z$ be an odd integer.


Then $x^n$ is called an odd power of $x$


Also known as

The expression $x^n$ is vocalised in a number of other ways:

  • the $n$th power of $x$
  • $x$ to the $n$th power
  • $x$ to the $n$th
  • $x$ to the $n$.


Knuth Uparrow Notation

In certain contexts in number theory, the symbol $\uparrow$ is used to denote the (usually) integer power operation:

$x \uparrow y := x^y$

This notation is usually referred to as Knuth (uparrow) notation.


Examples

Negative Power: $-3^{-3}$

$-3^{-3} = -\dfrac 1 {27}$


Also see


Historical Note

The concept of an integer power to a negative exponent was introduced by John Wallis in the $17$th century.


Sources

Retrieved from "https://proofwiki.org/w/index.php?title=Definition:Power_(Algebra)/Integer&oldid=692005"