#include <bits/stdc++.h>
using namespace std;
#define down 0.985
int lrj,n;
struct{
	double a,b,c;
	double operator[](double x)
	{
		return a*x*x+b*x+c;
	}
}a[10003];
double ans,sx;
inline double S(double x)
{
	double s=-1e145;
	for(int i=1;i<=n;i++)
	{
		s=max(s,a[i][x]);
	}
	return s;
}
inline void SA()
{
	double t=3000,nx;
	do{
		nx=sx+((rand()<<1)-RAND_MAX)*t;
		double s=S(nx);
		if(ans>s)
		{
			ans=s;
			sx=nx;
		}
		else
		{
			if(exp((s-ans)/t)*RAND_MAX<=rand())
			{
				sx=nx;
			}
		}
		t*=down;
	}while(t>1e-10);
}
signed main()
{
	srand(time(0));
	cin>>lrj;
	while(lrj--)
	{
		cin>>n;
		for(int i=1;i<=n;i++)
		{
			cin>>a[i].a>>a[i].b>>a[i].c;
		}
		sx=114.514;
		ans=S(sx);
		SA();
		printf("%.4lf\n",ans);
	}
	return 0;
}