Contents

# Contents

## Idea

In trigonometry the arccosine or “inverse cosine” is one of the inverse trigonometric functions.

## Definition

The arccosine is a section (or right inverse) to the cosine function cos, which in turn is one of the trigonometric functions. More precisely, it is the unique continuous section of the epimorphism in the (epi, mono) factorization of the cosine such that its value at $0$ is $\pi/2$ (see pi).