I believe when your teacher told you about "tableau" he meant arrays instead of tables.
So here is a startup you can use :
<html>
<head>
</head>
<title>Ex. 4</title>
<body bgcolor="Blue">
<script language=javascript>
var monTableauDePrenom = new Array(3);
monTableau [0] = "Prenom1";
monTableau [1] = "Prenom2";
monTableau [2] = "Prenom3";
var monTableauPlusGrand = new Array(4);
monTableauPlusGrand = ajouterPrenom(monTableauDePrenom);
//TODO afficher le tableau
function ajouterPrenom(monTableauDePrenom) {
var monTableau = new Array(4);
monTableau [0] = monTableauDePrenom [0]
monTableau [1] = monTableauDePrenom [1]
monTableau [2] = monTableauDePrenom [2]
monTableau [3] = "Prenom4";
return monTableau;
}
</SCRIPT>
</body>
</html>