1 #include <cmath>
 2 #include <cstdio>
 3 #include <iostream>
 4 #define PI acos(-1.0)
 5 //#define PI 3.1415926   不要用这个； 
 6 using namespace std;
 7 double num[10010];
 8 int main()
 9 {
10     int t;
11     scanf("%d", &t);
12     while(t--)
13     {
14         int m, n;
15         double max = 0.0;
16         scanf("%d %d", &m, &n);
17         n++;
18         for(int i=0; i<m; i++)
19         {
20             int ti;
21             scanf("%d",&ti);
22             num[i] = PI*ti*ti; 
23             if(num[i] > max)
24                 max = num[i];
25         }
26         double min=0.0, mid;
27         while(max - min > 1e-6)
28         {
29             mid=(max + min) / 2.0;
30             int total = 0;
31             for(int i=0; i<m; i++)
32                 total += (int)(num[i] / mid);
33             if(total >= n)
34                 min = mid;
35             else
36                 max = mid;
37         }
38         printf("%.4lf\n",mid);
39     }
40     return 0; 
41 }