<html>
<body>
<input id='argument' type="text"/>
<input id="cos" type="button" value="cos(x)"/>
<div id='res'></div>
<script type="text/javascript">
document.getElementById('cos').onclick = function(){
document.getElementById('res').innerHTML = Math.cos(document.getElementById('argument').value);
};
</script>
</body>
</html>