Did you try it please? it seems not to work
here is waht i have used
<!DOCTYPE html>
<html>
<head>
<style>
button { margin:4px; cursor:pointer; }
input { margin:4px; color:blue; }
</style>
<script src="http://code.jquery.com/jquery-latest.js"></script>
</head>
<body>
<div>
</div>
<script type= "text/Javascript">
$(document).ready(function() {
var value = $('#dropDown').val();
$('#textArea').hide();
if(value == 1)
{
($'#textArea').show();
}
});
</script>
<select name="dropDown" id="dropDown">
<option value="1"> No</option>
<option value="2">Yes</option>
</select>
<textarea name="text" id="textArea" /></textarea>
</body>
</html>