In the previous
section, we learned that functions passed
the vertical line test. There is another way to classify functions which
pass the **horizontal line test**. A function passes the horizontal
line test if
we draw a horizontal line anywhere in the domain of ,
and that line crosses
in at most one or less points. If a
function passes the horizontal line test then we call it
**one-to-one**, or
**1-1**.

In addition to being classified as one-to-one, we
can call
a
**polynomial** if
can be
written in the form

Each

There is one last classification of functions we are
going to talk about. A function is an **even** function if f(x)=f(-x).
This might be impossible you say, but take the function we just worked
with,

is an even function. x squared is equal
-x squared. So f(x) is an
even function. A function is **odd** if f(-x)=-f(x). Take for
example the
function f(x) = x.

f(x) is now odd.