program Project1;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
f,f1:text;
   d,l,n,i:integer;
   res:real;

   function len(d,l:integer):real;
   var
   b,a,res:real;
   begin
   if (l<d) then  len:=-1;
if (l=d) then len:=0;
if (l>d) then
begin
 b:=d+2*(l-d)/2;
 a:=2*(sqrt(sqr(l/2)-sqr(d/2)));
 res:=(a*b*pi)/4;
 len:=res;
 end;
   end;

begin
assign(f,'input.txt');
reset(f);
 assign(f1,'output.txt');
rewrite(f1);
readln(f,n);
for i:=1 to n do
begin
readln(f,d,l);
{if (l<d) then begin writeln(-1); readln; halt; end;
if (l=d) then begin writeln(0.0:0:3); readln; halt; end;
 b:=d+2*(l-d)/2;
 a:=2*(sqrt(sqr(l/2)-sqr(d/2)));
 res:=(a*b*pi)/4;}
   res:=len(d,l);
 writeln(f1,res:0:3);
     end;
 close(f);
 close(f1);
  end.