Question 393212
<pre><font face = "batangche" color = "indigo" size = 4><b>An ordered pair consists of the following things written in that order 

1. A left parentheses "("
2. A number, called the first coordinate, or x-coordinate
3. A comma
4. A number, called the second coordinate, or y-coordinate
5. A right parentheses ")"

Here are some examples of ordered pairs:

(7,4), (8,8) (5,1), (7,0), (0,0) etc.

Every ordered pair starts with a "(" on the left end, then a number,
then a comma, then another number, and finally a ")" on the right end.

A function is a set of ordered pairs, enclosed between braces { } such that no
two have the same first coordinate or x-coordinate.  It doesn't matter if two
have the same second coordinate or y-coordinate.  It would still be a function
as long as no two first coordinates are the same.

Here is a set of ordered pairs which model a function:

{ (<font color="red">7</font>,<font color="blue">2</font>), (<font color="red">1</font>,<font color="blue">1</font>), (<font color="red">8</font>,<font color="blue">1</font>), (<font color="red">4</font>,<font color="blue">2</font>), (<font color="red">3</font>,<font color="blue">11</font>) }

It models a function because all of the red numbers (first coordinates) are DIFFERENT.  It doesn't matter that some of the blue numbers (second coordinates)
are THE SAME.  It would still models a function whether any of the blue numbers
were the same or not. 

All we have to do to change that set of ordered pairs so that it DOES NOT
model a function is to change one or more of the red numbers so that two will
have the same first coordinates, (red number).  Like this:

{ (<font color="red">7</font>,<font color="blue">2</font>), (<font color="red">1</font>,<font color="blue">1</font>), (<font color="red">8</font>,<font color="blue">1</font>), (<font color="red">4</font>,<font color="blue">2</font>), (<font color="red">1</font>,<font color="blue">11</font>) }

I changed the last ordered pair (<font color="red">3</font>,<font color="blue">11</font>) to (<font color="red">1</font>,<font color="blue">11</font>).  That keeps the
set of five ordered pairs from modeling a function because it now has 
two ordered pairs with the same first coordinate <font color = "red">1</font>.

You can made them up by the hundreds.  Just put two or more ordered pairs
in it that have the same first coordinate, so that it will NOT model a function.
You can tell why it doesn't model a function by telling which first coordinates
are the same.

Edwin</pre>