1 /*
2 二分好题
3 */
4
5 // include file
6 #include <cstdio>
7 #include <cstdlib>
8 #include <cstring>
9 #include <cmath>
10 #include <cctype>
11 #include <ctime>
12
13 #include <iostream>
14 #include <sstream>
15 #include <fstream>
16 #include <iomanip>
17 #include <bitset>
18
19 #include <algorithm>
20 #include <string>
21 #include <vector>
22 #include <queue>
23 #include <set>
24 #include <list>
25 #include <functional>
26
27 using namespace std;
28
29 // typedef
30 typedef long long LL;
31 typedef unsigned long long ULL;
32 typedef __int64 Bint;
33
34 //
35 #define read freopen("in.txt","r",stdin)
36 #define write freopen("out.txt","w",stdout)
37 #define FORi(a,b,c) for(int i=(a);i<(b);i+=c)
38 #define FORj(a,b,c) for(int j=(a);j<(b);j+=c)
39 #define FORk(a,b,c) for(int k=(a);k<(b);k+=c)
40 #define FORp(a,b,c) for(int p=(a);p<(b);p+=c)
41 #define FORii(a,b,c) for(int ii=(a);ii<(b);ii+=c)
42 #define FORjj(a,b,c) for(int jj=(a);jj<(b);jj+=c)
43 #define FORkk(a,b,c) for(int kk=(a);kk<(b);kk+=c)
44
45 #define FF(i,a) for(int i=0;i<(a);i++)
46 #define FFD(i,a) for(int i=(a)-1;i>=0;i--)
47
48 #define Z(a) (a<<1)
49 #define Y(a) (a>>1)
50
51 const double eps = 1e-6;
52 const double INFf = 1e10;
53 const int INFi = 1000000000;
54 const double Pi = acos(-1.0);
55
56 template<class T> inline T sqr(T a){return a*a;}
57 template<class T> inline T TMAX(T x,T y)
58 {
59 if(x>y) return x;
60 return y;
61 }
62 template<class T> inline T TMIN(T x,T y)
63 {
64 if(x<y) return x;
65 return y;
66 }
67 template<class T> inline void SWAP(T &x,T &y)
68 {
69 T t = x;
70 x = y;
71 y = t;
72 }
73 template<class T> inline T MMAX(T x,T y,T z)
74 {
75 return TMAX(TMAX(x,y),z);
76 }
77
78
79 // code begin
80 #define MAXN 10010
81 int T,N,F;
82 double R[MAXN],ans;
83 bool Isok(double lt)
84 {
85 int cnt = 0;
86 FORi(0,N,1)
87 {
88 cnt += (int)((Pi*R[i]*R[i])/lt);
89 if(cnt>=F+1) return true;
90 }
91 return false;
92 }
93 int main()
94 {
95 read;
96 write;
97 scanf("%d",&T);
98 while(T--)
99 {
100 scanf("%d %d",&N,&F);
101 FORi(0,N,1)
102 {
103 scanf("%lf",&R[i]);
104 }
105 double LL = 0,RR = Pi*MAXN*MAXN;
106 while( RR-LL>eps)
107 {
108 double mid = (LL+RR)/2;
109 if(Isok(mid))
110 {
111 LL = mid;
112 }
113 else
114 {
115 RR = mid;
116 }
117 }
118 printf("%.4f\n",LL);
119 }
120 return 0;
121 }
