holiday/8.21/B-Light/main.cpp

#include <iostream>
#include<cstdio>
#include<algorithm>
#include <cmath>
using namespace std;
const double eps= 1e-5;
double H,h,D;
double f(double d)
{
	return D-d+H-(H-h)*D/d;
//	return D-d+h-(H-h)*(D-d)/d;
}
double sanfen(double l,double r)
{
	double mid,midr,ans;
	while(fabs(r-l)>eps)
	{
		mid=(l+r)/2;
		midr=(mid+r)/2;
		if(f(mid)<f(midr))l=mid;
		else r=midr;
	}
	return f(l);
}
int main()
{
	int t;
	scanf("%d",&t);
	while(t--)
	{
		scanf("%lf%lf%lf",&H,&h,&D);
		printf("%.3lf\n",sanfen(D-D*h/H,D));
	}
	return 0;
}