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The Euler Equation

Numbers | A History of Numbers | Propositional Logic | Logical Completeness | The Liar's Paradox
Logical Consistency | Basic Methods of Mathematical Proof | Integers and Natural Numbers
Rational Numbers | Irrational Numbers | Imaginary Numbers | The Euler Equation

The Euler (pronounced oiler) Equation must surely rate as one of the most elegant, beautiful and awe-inspiring formulae in maths. Its consequences are diverse and shocking when you consider its simplicity.

The Euler Equation is often given by the following:

eiθ = cos θ + i sin θ

Where e and i are the standard constants defined by:

d/dx ex = ex
i2 = -1

And θ is any angle in radians.

Origins of the Euler Equation

Let us consider the function:

y = cos x + i sin x

Continuing to treat i like any other number, we have, by differentiation:

dy/dx = -sin x + i cos x = i(cos x + i sin x)
=> dy/dx = iy
=> i dx/dy = 1/y
=> ix = ln y + c

But when x = 0, y = 1. So c = 0.

=> ix = ln y
=> y = eix
So cos x + i sin x = eix

It may be objected that we have nowhere defined the meaning of a number such as ez when z is complex; but the reader should not be deterred by such inhibitions. Indeed, the above paragraph may be regarded as providing, if not a definition, at least a reasonable exposition of the meaning of eix, making it consistent with the familiar processes of mathematics.

Consequences of the Euler Equation

One of the most fundamental consequences of the Euler Equation is shown by taking θ to equal π radians. When this is done then the equation (once rearranged slightly) gives the following:

eπi + 1 = 0

This unites the five most important numbers in maths; π, i, e, 1 and 0 into one relation and so the Euler Equation is taken as one of the most important points of unification. From this equation one gains a glimmer of how the whole of maths fits together.

This glimmer is reinforced if one takes the natural log of both sides of the equation (after subtracting one from both sides). This allows us to define the natural log of the negative numbers in the complex plane as follows:

ln -1 = iπ

A far reaching result which defines a whole family of hyperbolic (or modular) forms (strongly related to hyperbolic functions) based around two mutually perpendicular complex planes (represented commonly by Argand Diagrams) sharing no axes. These were linked to another, seemingly unrelated, part of maths known as elliptic curves by the Taniyama-Shimura theorem which (as the first part of the Langland's Programme) became part of the quest for a Grand Unified Mathematics and forms the basis for some of the most important maths today. Indeed, the famed proof of Fermat's Last Theorem by Andrew Wiles was in fact also the proof of Taniyama-Shimura and so became dually celebrated as a triumph over an amateur tease-artist and as the stabilisation of an increasingly shaky foundation of an entire branch of maths.

Not bad for such a simple equation.

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Entry Data
Entry ID: A346295 (Edited)

Written and Researched by:
Joe aka Arnia, Muse, Keeper, MathEd, Guru and Zen Cook (business is booming)

Edited by:
26199

Date: 30   June   2000

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 Referenced Guide Entries Numbers Imaginary Numbers Propositional Logic A History of Numbers Basic Methods of Mathematical Proof Integers and Natural Numbers Rational Numbers Logical Completeness Logical Consistency Irrational Numbers The Liar's Paradox Fermat's Last Theorem Leonhard Euler - Mathematician

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Most of the content on h2g2 is created by h2g2's Researchers, who are members of the public. The views expressed are theirs and unless specifically stated are not those of the BBC. The BBC is not responsible for the content of any external sites referenced. In the event that you consider anything on this page to be in breach of the site's House Rules, please click here. For any other comments, please start a Conversation above.