#include<cstdio>

#include<cstring>

#include<algorithm>

#include<cmath>

#define db double

using namespace std;

const db eps=1e-;

int T;db a,b,l,r;

db f(db x){return sqrt((-x*x/a)*b);}

db cal(db l,db r){return (f(l)+*f((l+r)/)+f(r))*(r-l)/;}

db simp(db l,db r,db eps,db ret)

{

  db mid=(l+r)/,vl=cal(l,mid),vr=cal(mid,r);

  if(fabs(vl+vr-ret)<=*eps)return vl+vr+(vl+vr-ret)/;//not ret+()/15

  return simp(l,mid,eps/,vl)+simp(mid,r,eps/,vr);

}

int main()

{

  scanf("%d",&T);

  while(T--)

    {

      scanf("%lf%lf%lf%lf",&a,&b,&l,&r);

      a*=a;b*=b;

      printf("%.3lf\n",simp(l,r,eps,cal(l,r))*);

    }

  return ;

}