Definition:Inverse Sine/Complex/Definition 2

Definition

Let $z \in \C$ be a complex number.

The inverse sine of $z$ is the multifunction defined as:

$\sin^{-1} \paren z := \set {\dfrac 1 i \ln \paren {i z + \sqrt {\cmod {1 - z^2} } \exp \paren {\dfrac i 2 \arg \paren {1 - z^2} } } + 2 k \pi: k \in \Z}$

where:

$\sqrt {\cmod {1 - z^2} }$ denotes the positive square root of the complex modulus of $1 - z^2$

$\arg \paren {1 - z^2}$ denotes the argument of $1 - z^2$

$\ln$ is the complex natural logarithm considered as a multifunction.

Also defined as

In expositions of the inverse trigonometric functions, it is frequently the case that the $2 k \pi$ constant is ignored, in order to simplify the presentation.

It is also commonplace to gloss over the multifunctional nature of the complex square root, and report this definition as:

$\sin^{-1} \paren z := \dfrac 1 i \ln \paren {i z + \sqrt {1 - z^2} }$

Also see

• Equivalence of Definitions of Complex Inverse Sine Function

• Definition:Complex Arcsine

• Definition:Inverse Hyperbolic Sine/Complex/Definition 2