The *inverse cosine* of , denoted by
,
is defined as the unique value
satisfying
.
The inverse cosine function ``
'' is also known as
the *arccosine* function ``.''

**Domain and range of .**
and
.

**Trigonometric equation.**
Consider the solutions
in the cycle to the equation
.
By observing
,
we obtain the two solutions and as

and

Department of Mathematics