# Archimedean spiral

From JSXGraph Wiki

It can be described in polar coordinates [math](r, \theta)[/math] by the equation

- [math]\, r=a+b\theta[/math]

with real numbers [math]a[/math] and [math]b[/math].

### The JavaScript code to produce this picture

```
var board = JXG.JSXGraph.initBoard('jxgbox', {boundingbox: [-10, 10, 10, -10]});
var a = board.create('slider', [[1,8],[5,8],[0,1,4]],{name:'a'});
var b = board.create('slider', [[1,9],[5,9],[0,0.25,4]],{name:'b'});
var c = board.create('curve', [function(phi){return a.Value()+b.Value()*phi; }, [0, 0],0, 8*Math.PI],
{curveType:'polar', strokewidth:4});
var g = board.create('glider', [c]);
var t = board.create('tangent', [g], {dash:2,strokeColor:'#a612a9'});
var n = board.create('normal', [g], {dash:2,strokeColor:'#a612a9'});
```