pku 1799 yeehaa

推出推导式：r=R*sin(PI/n)/(1+sin(PI/n))。

code:

#include <iostream>
#include <cstdio>
#include <cmath>
#define PI 3.1415926
using namespace std;

int main()
{
    int cas;
    while(scanf("%d",&cas)!=EOF)
    {
      int n, t=1;
      double R, r;
      while(cas--)
      {
        scanf("%lf%d",&R, &n);
        r=R*sin(PI/n)/(1+sin(PI/n));
        printf("Scenario #%d:\n%.3lf\n\n",t++, r);
      }
    }
    return 0;
}