Program pie;
const
   lef=0.00001;
var
   t,n,f,i,j:longint;
   r:array[1..10000] of longint;
   s:array[1..10000] of double;
   maxs:double;
procedure sort(l,r:double);
var
   m:real;
   i,j,tot:longint;
begin
   m:=(l+r)/2;
   tot:=0;
   for i:=1 to n do inc(tot,trunc(s[i]/m));

   if tot>=f then
   begin
      if r-l<lef then writeln(r:4:4)
      else sort(m,r);


   end
   else sort(l,m);










end;
begin
   read(t);
   while (t>0) do
   begin
      read(n,f);
      inc(f);
      for i:=1 to n do
      begin
         read(r[i]);
         s[i]:=sqr(r[i])*pi;
      end;
      maxs:=s[1];
      for i:=2 to n do
         if maxs<s[i] then maxs:=s[i];
      sort(0,maxs);

      dec(t);
   end;
end.