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

**Domain and range of .**
and
.

**Trigonometric equation.**
Consider the solutions to the equation
in the interval (which is the *two* cycle
for the tangent function).
The two solutions and are given by

Note that if we find that and are out of the interval .

Department of Mathematics