<html>
<script>
function activarcasilla(check){
if(document.x.check.checked==true){
document.x.b1.style.visibility="visible";
}else{
document.x.b1.style.visibility="hidden";
}
}
</script>
<head>
<title></title>
</head>
<body>
<p align="center">
<body>
</p>
<form name="x">
<input name="check" type="checkbox" id="check" value="checkbox" onclick="activarcasilla(this)">
<input name="b1" type="submit" value="enviar" style="visibility:hidden;">
</form>
</body>
</body>
</html>