Question 68533
<pre><font size = 5><b>Is this a function?:
f(x) = 2 if x > 1
f(x) = -1 otherwise

Let's graph it and see:

{{{ graph( 200, 200, -4, 4, -4, 4, 2*sqrt(x-1)/sqrt(x-1), -1*sqrt(1-x)/sqrt(1-x)) }}}

It passes the vertical line test. That is,
no point on the graph is directly above or 
directly below any other point on the graph.
So it is a function.

Edwin</pre>