The function is
.
Determine whether the function
is a one to one or not for all
using horizontal line test.
Graph the function
.

Observe the graph :
\Draw the horizontal line
, this horizontal line touches the graph twice.
The function is not an one-to-one, because it violates the horizontal line test.
\Consider
.
Graph the function on the
.
Observe the graph :
\Draw the horizontal line
.
The horizontal line does not touch the graph more than once.
\The function is a one-to-one, because it passes the horizontal line test.
\Assume
.
Find
.
If
then
.
Consider
.
Differentiate on each side with respect to
.

Trigonometric identity:
.

Therefore,
.
Substitute
in above expression.
.
The function is not an one-to-one for all
.
The function is a one-to-one on
.
Derivative of the
is
.