# Fermat's spiral

From JSXGraph Wiki

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

- [math]r = \pm a\theta^{1/2}\,[/math]

with a real number [math]a[/math].

### The JavaScript code to produce this picture

```
var board = JXG.JSXGraph.initBoard('jxgbox', {boundingbox: [-10, 10, 10, -10]});
var a = board.create('slider', [[1,9],[5,9],[0,1,4]],{name:'a'});
var c1 = board.create('curve', [function(phi){return a.Value()*Math.sqrt(phi); }, [0, 0],0, 8*Math.PI],
{curveType:'polar', strokewidth:4});
var c2 = board.create('curve', [function(phi){return -a.Value()*Math.sqrt(phi); }, [0, 0],0, 8*Math.PI],
{curveType:'polar', strokewidth:4});
```