# How do you evaluate #cos^-1(cos((19pi)/10))#?

##### 1 Answer

Aug 31, 2016

#### Explanation:

Use that, if f is a single valued function,

Here, it is

Disambiguation note on uniqueness, despite the convention

that the inverse trigonometric function values are defined as

principal values:

If f is a single-valued function operator, in

coupled operation

and the ordered couple operation

Despite that f might not be bijective, being single-valued, it is

bijective in an infinitesimal neighborhood

So there is unique answer for single-valued function under these

twin operations.

This note is important for applications wherein