#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;
typedef long long ll;
const double eps=1e-10;

double a,b,l,r;
inline double F(double x){
    return sqrt((a*a-x*x)/(a*a))*b;
}
inline double cal(double l,double r){
    return (F(l)+F(r)+4*F((l+r)/2))*(r-l)/6;
}
double Simpson(double l,double r,double now){
    double mid=(l+r)/2,p=cal(l,mid),q=cal(mid,r);
    if(abs(now-p-q)<eps) return now;
    else return Simpson(l,mid,p)+Simpson(mid,r,q);
}

int main(int argc, const char * argv[]) {
    int T;scanf("%d",&T);
    while(T--){
        scanf("%lf%lf%lf%lf",&a,&b,&l,&r);
        l=max(l,-a);r=min(r,a);
        printf("%.3f\n",2*Simpson(l,r,cal(l,r)));
    }

    return 0;
}