哪里错了呢，我想了半天也没有想到？求大佬解答

<script type="text/javascript">

  function  app2(x,y)

  { var sum,x,y;

    sum = x * y;

    return sum;

  }

  var req1,req2,sumq;

 req1=sum(5,6);

 req2=sum(2,3);

 sumq=req1+req2;

document.write("req1的值:"+req1+"<br/>");

document.write("req2的值:"+req2+"<br/>");

document.write(req1+"与"+req2+"和:"+sumq);

</script>