HDU 2289 Cup

#include <cstdio>    
#include <cmath>  
#include <algorithm>  
using namespace std;  
#define PI 3.1415926535897932384626 
#define exp 1e-9  
double solve(double r,double R,double h,double H)  
{  
    double u = h/H*(R-r) + r;  
    return PI/3*(r*r+r*u+u*u)*h;  
}  
int main()  
{  
    int t;  
    double r,R,H,V,mid,vv,f,l;  
    scanf("%d",&t);  
    while(t--)  
    {  
        scanf("%lf%lf%lf%lf",&r,&R,&H,&V);  
        f=0;  
        l=100;  
        while(l-f>exp)  
        {  
            mid=(l+f)/2;  
            vv=solve(r,R,mid,H);  
            if(fabs(vv-V)<=exp)  
                break;  
            else if(vv>V)  
                l=mid-exp;  
            else  
                f=mid+exp;  
        }  
        printf("%.6lf\n",mid);  
    }  
    return 0;  
}