1100C NN and the Optical Illusion

推公式，水题。cos（）函数是默认弧度制的

 1 #include <iostream>
 2 #include <cstring>
 3 #include <string>
 4 #include <map>
 5 #include <set>
 6 #include <algorithm>
 7 #include <fstream>
 8 #include <cstdio>
 9 #include <cmath>
10 #include <stack>
11 #include <queue>
12 using namespace std;
13 const double Pi=3.14159265358979323846;
14 typedef long long ll;
15 
16 int main()
17 {
18     double n,a;
19     cin>>n>>a;double s=360/n*1.0/180*Pi;
20     double ans=(sqrt(2)*a)/(sqrt(2)-sqrt(1-cos(s)))-a;    
21     printf("%.7lf\n",ans);
22     return 0;
23  }