## WeBWorK Main Forum

### parametric plots

by joel robbin -
Number of replies: 2
The Wiki page at

https://webwork.maa.org/wiki/ParametricPlots

shows how to draw a circle using parametric equations.
How do I add the tangent line?

The following code almost works,
but the tangent line is drawn vertical.

$gr = init_graph(-1.5,-1.5,1.5,1.5, 'axes'=>[0,0]); #'grid' => [30,30], #'pixels' => [400,400]);$xfunc = sub {
my $t = shift(); if ($t<0) {
return $t+1; } else { return cos($t);
}
};

$yfunc = sub { my$t = shift();
if ($t<0) { return (3.0/4.0)*($t+1)-(25.0/4.0);
} else {
return sin($t); } };$fn = new Fun( $xfunc,$yfunc, $gr );$fn->domain(-1.0,6.2832);

### Re: parametric plots

by joel robbin -
My code got truncated and had a bug. (I tried
to do a case analysis in code and in between
the cases a spurious line was drawn.) However,
it should be possibly to just add another function
to the graph object, and I couldn't figure out how
to do this.

### Re: parametric plots

by Michael Gage -
(it's the &lt; sign that was interpreted as an HTML markup that caused the trouble in the post. )

To add two functions use this construction

$fn = new Fun($xfunc, $yfunc,$gr );
$fn2 = new Fun($xfunc2, $yfunc2,$gr );

which adds two Function objects to the graph $gr and also "stores" those objects in$fn and \$fn2.

Both functions will be plotted by the graph.

More documentation can be found at:

http://webwork.maa.org/doc/cvs/pg_CURRENT/

under

Libraries: Fun and WWPlot

Macros: PGgraphmacros.pl

-- Mike