1 #include <cstdio>
 2 #include <cmath>
 3 #include <iostream>
 4 #include <algorithm>
 5 using namespace std;
 6 
 7 double pi = acos(-1.0);
 8 int N,F,t;
 9 double v[11111];
10 
11 int main()
12 {
13     int T;
14     int N,F;
15     int i;
16     int r;
17     double left,right,mid;
18     double v[10011];
19 
20 
21     scanf("%d",&T);
22     while(T--)
23     {
24         scanf("%d%d",&N,&F);
25         F++;//加上自己
26         right = 0;
27         for(i=0; i<N; i++)
28         {
29             scanf("%d",&r);
30             v[i] = pi * r * r;
31             right = max(right, v[i]);//找出面积最大的饼，为二分上界
32         }
33         left=0;
34         mid=(left + right) / 2;
35         while(right - left >= 0.0000001)//精度要求
36         {
37             t=0;
38             for(i=0; i<N; i++) t += (int)(v[i]/mid);
39             if(t >= F)
40             left = mid;
41             else
42             right = mid;
43             mid = (left + right) / 2;
44         }
45         printf("%0.4lf\n",mid);
46     }
47     return 0;
48 }