Cosecant of Complex Number
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Theorem
Let $a$ and $b$ be real numbers.
Let $i$ be the imaginary unit.
Then:
- $\csc \paren {a + b i} = \dfrac {\sin a \cosh b - i \cos a \sinh b} {\sin^2 a \cosh^2 b + \cos^2 a \sinh^2 b}$
where:
- $\csc$ denotes the complex cosecant function.
- $\sin$ denotes the real sine function
- $\cos$ denotes the real cosine function
- $\sinh$ denotes the hyperbolic sine function
- $\cosh$ denotes the hyperbolic cosine function
Proof
\(\ds \csc \paren {a + b i}\) | \(=\) | \(\ds \frac 1 {\sin \paren {a + b i} }\) | Definition of Complex Cosecant Function | |||||||||||
\(\ds \) | \(=\) | \(\ds \dfrac 1 {\sin a \cosh b + i \cos a \sinh b}\) | Sine of Complex Number | |||||||||||
\(\ds \) | \(=\) | \(\ds \dfrac {\sin a \cosh b - i \cos a \sinh b} {\paren {\sin a \cosh b - i \cos a \sinh b} \paren {\sin a \cosh b + i \cos a \sinh b} }\) | multiplying denominator and numerator by $\sin a \cosh b - i \cos a \sinh b$ | |||||||||||
\(\ds \) | \(=\) | \(\ds \dfrac {\sin a \cosh b - i \cos a \sinh b} {\sin^2 a \cosh^2 b - i^2 \cos^2 a \sinh^2 b}\) | Difference of Two Squares | |||||||||||
\(\ds \) | \(=\) | \(\ds \dfrac {\sin a \cosh b - i \cos a \sinh b} {\sin^2 a \cosh^2 b + \cos^2 a \sinh^2 b}\) | Definition of Imaginary Unit |
$\blacksquare$