The cosine function and inverse cosine (or arccosine) function
The arccosine function is a reflection of the cosine function about the line
Source
Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:
"Algebra and Trigonometry."
http://cnx.org/contents/13ac107a-f15f-49d2-97e8-60ab2e3b519c@5.241
OpenStax
CC BY 4.0.