Cosine
Domain, codomain and image
Domain	(−∞,∞) a
Codomain	[−1,1] a
Basic features
Parity	even
Period	2π
Specific values
At zero	1
Maxima	(2kπ, 1) b
Minima	((2k − 1)π, −1)
Specific features
Root	kπ - π/2
Critical point	kπ
Inflection point	kπ - π/2
Fixed point	0.739085 (Dottie number) [1]
a For real (i.e. non- complex) numbers. b Variable k is an integer.

The cosine (abbreviated cos) is a trigonometric function of an angle, which is defined in a triangle as the ratio of the length of the adjacent side to the length of the hypotenuse. ^[2] In our case

${\displaystyle \cos A={\frac {\textrm {adjacent}}{\textrm {hypotenuse}}}={\frac {b}{h}}.}$

The reciprocal of cosine is defined as the secant function. (Similarly, the reciprocal of sine is cosecant)

The inverse of the cosine function is known as the arccosine, represented ${\displaystyle arccos(x)}$ or ${\displaystyle cos^{-1}(x)}$.

https://es.wikipedia.org/wiki/Coseno