/*hdu 1724 Ellipse simpson积分求椭圆的部分面积simpson积分法 http://zh.wikipedia.org/zh-tw/%E8%BE%9B%E6%99%AE%E6%A3%AE%E7%A7%AF%E5%88%86%E6%B3%95*/#include
    
     #include
     
      const double eps=1e-8;inline double jue(double a){	return a>0?a:-a;}int dbcmp(double a){	if(a>eps)return 1;	if(a<(-eps)) return -1;	return 0;}template
      
       inline T sqr(T d){return d*d;}double a,b;inline double func(double x){	return 2*b*sqrt(1-sqr(x)/sqr(a));}double simpson(double l,double r){	return (func(l)+func(r)+4*func((l+r)/2))/6*(r-l);}double work(double l,double r){	double mid=(l+r)/2;	double ans=simpson(l,r);	if(dbcmp(ans-simpson(l,mid)-simpson(mid,r))==0)	{		return ans;	}else	{		return work(l,mid)+work(mid,r);	}}int main(){	int n;	double l,r;	scanf("%d",&n);	while(n--)	{		scanf("%lf%lf%lf%lf",&a,&b,&l,&r);		double ret=work(l,r);		printf("%.3f\n",ret);	}	return 0;}