#include<bits/stdc++.h>
using namespace std;
#define eps 1e-12
double H,h,D;
double f(double x){
	return D-x+H-(H-h)*D/x;
}
signed main(){
	int t,i;
	cin>>t;
	while(t--){
		cin>>H>>h>>D;
		double l=(H-h)/H*D,r=D,m1,m2;
		while(l+eps<=r){
			m1=l+(r-l)/3.0;
			m2=l+(r-l)/1.5;
			if(f(m1)>=f(m2)){
				r=m2;
			}else{
				l=m1;
			}
		}
		printf("%.3f\n",f(l));
	}
	return 0;
}