第二个方法用不了，有没有大神解答解答我错哪了啊
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>二维数组</title>
<script type="text/javascript">
var marr = [[0 , 1 , 2 ],[1 , 2 , 3]];
marr[2][2]=2*5;
marr[2][1]=marr[2][2]+1;
document.write("marr[2][2]是:"+ marr[2][2]+'<br> ');
document.write("marr[2][1]是:"+marr[2][1]);
</script>
</head>
<body>
</body>
</html>
第二个方法用不了，有没有大神解答解答我错哪了啊
