Euler's formula or Euler's formula , named after Leonhard Euler , or Euler's relation in some sources , is an equation that represents a fundamental connection between the trigonometric functions and the complex exponential functions using complex numbers .
Euler's formula denotes the equation that is valid for everyone
As a consequence of Euler's formula, the equation results for all of them
Derivation by means of series expansion
Euler's formula can be calculated from the Maclaurin series of functions and , , derive
The transformations are based on
For , the so-called Euler's identity results from Euler's formula
which establishes a simple connection between four of the most important mathematical constants : Euler's number , the circle number , the imaginary unit and the real unit . The following modified variant of the equation is sometimes preferred - although more complicated - because it adds another mathematically significant constant with zero :
If one extends the definition of the numerical value as a limit value to the complex numerical level , the result is correspondingly for the value . The animation on the right shows the intermediate results of the calculation of the expression , which are connected to a segment in the complex plane : It shows that this segment assumes the shape of an arc, the left end of which actually approaches the number on the real axis.
Relationship between exponentials and trigonometric functions
Sine and cosine result from the real part and the imaginary part of the complex exponential function.
The imaginary part is obtained by calculating:
The Euler formula allows a completely new view of the trigonometric functions, since the functions sine and cosine , which are used in conventional trigonometry only with real arguments, now also have a meaning in complex analysis.
The formulas for the real and imaginary part result from:
A consequence of the connection of trigonometric functions and exponential functions from the Euler formula is Moivresche's theorem (1730).
Providing the sines and cosines with imaginary arguments, a bridge to the hyperbolic functions is built :
As can be seen, the two functions obtained correspond exactly to the definitions of the hyperbolic sine and hyperbolic cosine .
Based on this, Euler's formula can also be used to solve numerous other problems, for example when calculating the power of the imaginary unit with itself. Although the result obtained is ambiguous, all individual solutions remain in the real area with a main value of
A practically important application of Euler's formula can be found in the field of alternating current technology , namely in the investigation and calculation of alternating current circuits with the help of complex numbers.
Euler's formula first appeared in Leonhard Euler's two-volume Introductio in analysin infinitorum in 1748 under the premise that the angle is a real number. However, this restriction soon turned out to be superfluous, because Euler's formula applies equally to all real and complex arguments. This results from Euler's formula with a real argument in connection with the identity theorem for holomorphic functions .
Before that, Roger Cotes published an incorrect mathematical connection in 1714, which is similar to Euler's formula.
In modern notation it looks like this:
where a circle with a radius fixed in the coordinate origin and an angle between the x-axis and a ray that intersects the origin are considered.
The imaginary unit should be on the other side of the equation.
- Roger Cotes: Logometria . Philosophical Transactions of the Royal Society of London ,. 1714, p. 32 (Latin, hathitrust.org ).