Calculators

Given a circle with radius r =

Code for the form above:

<form name="aform" onSubmit="document.aform.area.value=3.1415926 * document.aform.radius.value * document.aform.radius.value; return false;">

Given a circle with radius <i>r</i> =
<input name=radius type=text size="10" value="2" >
<p>
<input type="submit" value="calculate area ->">
<input name=area type=text size="10">

</form>