FZU 2099 魔法阵（计算几何）

#include <iostream>
#include <string.h>
#include <stdlib.h>
#include <algorithm>
#include <math.h>
#include <stdio.h>

using namespace std;
double l,r;
double ans;
double pi=2*asin(1.0);
int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%lf%lf",&l,&r);
        if(r>=l/sqrt(3.0))
            ans=pi*r*r;
        else if(r<=l/3.0)
            ans=sqrt(3.0)/3.0*l*l;
        else
        {
            double date=16*r*r-4.0/3.0*l*l;
            double x=(2*l-sqrt(date))/8;
            double s2=2*x*(l/sqrt(3.0))*1.0/2;
            double s3=pi*r*r*asin(x/r)/pi;
            double s4=s2-s3;
            ans=pi*r*r+s4*6;
        }
        printf("%.2f\n",ans);
    }
    return 0;
}