<html>
<body>
<script>
function area(radius)
{
var area;
area=Math.PI*radius*radius;
return area;
}
</script>
<form>
enter the radius:
<input type="text" name="radius"> <br> <br>
Area <input type="text" name="result">
<input type="button" value="calculate" onclick="result.value=area(radius.value)">
</form>
</body>
</html>
