1 #include <iostream>

 2 #include <stdio.h>

 3 #include <math.h>

 4 using namespace std;

 5 double pi = acos(-1.0);

 6 int F,N;

 7 double V[10001];

 8 bool test(double x)

 9 {

10     int num=0;

11     for(int i = 0; i < N;i++)

12     {

13         num += int(V[i]/x);

14     }

15     if(num>=F)

16     return true;

17     else return false;

18 }

19 int main()

20 {

21     int t,r;

22     double v,max,left,right,mid;

23     scanf("%d",&t);

24     while(t--)

25     {

26         scanf("%d%d",&N,&F);

27         F = F+1;

28         for(int i = 0; i < N; i++)

29         {

30             scanf("%d",&r);

31             V[i] = pi*r*r;

32             v += V[i];

33         }

34         max = v/F;

35         left = 0.0;

36         right = max;

37         while((right-left)>1e-6)//注意这里的精度问题。

38         {

39             mid = (left+right)/2;

40             if(test(mid))

41             left = mid;

42             else right = mid;

43         }

44         printf("%.4f\n",mid);

45     }

46     return 0;

47 }