cis (mathematics)

$cis$ is a mathematical notation defined by $cis x = cos x + i sin x$ , where $cos$ is the cosine function, $i$ is the imaginary unit and $sin$ is the sine function. $x$ is the argument of the complex number (angle between line to point and x-axis in polar form). The notation is less commonly used in mathematics than Euler's formula, $e ix$ , which offers an even shorter notation for $cos x + i sin x$ , but cis(x) is widely used as a name for this function in software libraries.

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