我用eclipse做的输入边长求面积为什么不能运行，谁能帮我改下
<%@ page language="java" contentType="text ml; charset=GBK"pageEncoding="GBK"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.
<html>
<head>
<meta http-equiv="Content-Type" content="text ml; charset=GBK">
<title>Insert title here</title>
</head>
<body>
<p>请输一条边长：</p>
<form method="get"name="form">
<input type="text" name="radius1">
<p>请输一条边长：</p>
<input type="text" name="radius2">
<p>请输一条边长：</p>
<input type="text" name="radius3">
<input type="submit"name="submit"value="开始计算">
</form>
<%
String a=request.getParameter("radius1");
if(a<0)
out.print("你输入的数字有误，请重新输入");
else
Double f=Double.parseDouble(a);
String b=request.getParameter("radius2");
if(b<0)
out.print("你输入的数字有误，请重新输入");
String c=request.getParameter("radius3");
if(c<0)
out.print("你输入的数字有误，请重新输入");
String d=(a+b+c)/2;
if(a+b>c&&a+c>b&&b+c>a){
float s=Math.sqrt(d*(d-b)*(d-c)(d-a));
out.print(s);
}
else
out.print("你输入的三个数不能构成三角形，请重新输入");
%>
</body>
</html>
