# Archimedean spiral

It can be described in polar coordinates $\displaystyle{ (r, \theta) }$ by the equation

$\displaystyle{ \, r=a+b\theta }$

with real numbers $\displaystyle{ a }$ and $\displaystyle{ b }$.

### The JavaScript code to produce this picture

<link rel="stylesheet" type="text/css" href="http://jsxgraph.uni-bayreuth.de/distrib/jsxgraph.css" />
<script type="text/javascript" src="http://jsxgraph.uni-bayreuth.de/distrib/prototype.js"></script>
<script type="text/javascript" src="http://jsxgraph.uni-bayreuth.de/distrib/jsxgraphcore.js"></script>
<div id="jsxgbox" class="jxgbox" style="width:500px; height:500px;"></div>

 board = JXG.JSXGraph.initBoard('jsxgbox', {originX: 250, originY: 250, unitX: 50, unitY: 50});
var a = board.createElement('slider', [[1,8],[5,8],[0,1,4]]);
var b = board.createElement('slider', [[1,9],[5,9],[0,0.25,4]]);
var c = board.createElement('curve', [function(phi){return a.Value()+b.Value()*phi; }, [0, 0],0, 8*Math.PI],
{curveType:'polar', strokewidth:4});
var g = board.createElement('glider', [c]);
var t = board.createElement('tangent', [g], {dash:2,strokeColor:'#a612a9'});
var n = board.createElement('normal', [g], {dash:2,strokeColor:'#a612a9'});