hdu 6158 计算几何

#include<bits/stdc++.h>
using namespace std;
const double eps=1e-13;
const double PI=acos(-1.0);
int main()
{
    int t,r1,r2,n;
    scanf("%d",&t);
    while(t--&&scanf("%d%d%d",&r1,&r2,&n)!=EOF)
    {
        if(r1<r2) 
            swap(r1,r2);
        double k1=-1.0/r1,k2=1.0/r2,k3=1.0/(r1-r2);
        double k4=k1 + k2 + k3;
        double ans=(r1-r2)*(r1-r2);
        n--;
        for(int i=1;i<=n;i+=2)
        {
            double r4=1.0/k4;
            if(r4*r4<eps)
                break;
            ans+=r4*r4;
            if(i+1<=n) 
                ans+=r4*r4;
            double k5=2*(k1+k2+k4)-k3;
            k3=k4;
            k4=k5;
        }
        printf("%.5f\n",ans*PI);
    }
    return 0;
}