Question 720966
<pre>
f(x) = {{{system(matrix(2,3,

red(2x+1),",",red(x>=1),
green(x/2-3),",",green(x<1)))}}}

The graph of y=2x+1 is the red line.
It is drawn solid to the right of where x=1
The graph of y={{{x/2}}}-3 is the green line
It is drawn solid to the left of where x=1.

{{{drawing(300,400,-7,5,-6,10,
graph(300,400,-7,5,-6,10,(2x+1)*(

sqrt(sin(12x))/sqrt(sin(12x))
)),red(line(1,3,16,33)),
graph(300,400,-7,5,-6,10,21,(x/2-3)*(

sqrt(sin(12x))/sqrt(sin(12x))
)), green(line(-16,-11,1,-2.5))


  )}}}

We erase the dotted parts:

{{{drawing(300,400,-7,5,-6,10,red(line(1,3,16,33)),
graph(300,400,-7,5,-6,10), green(line(-16,-11,1,-2.5))


  )}}}

The red line includes the endpoint (1,3), so we place
a darkened circle at (1,3).  The green line does not
include the endpoint (1,-2.5) so we draw an open circle
there:

{{{drawing(300,400,-7,5,-6,10,red(line(1,3,16,33)),
graph(300,400,-7,5,-6,10), green(line(-16,-11,.8,-2.6)),
red(circle(1,3,.15),circle(1,3,.1),circle(1,3,.2)), green(circle(1,-2.5,.2))


  )}}}

  Edwin</pre>