QUADAREA.cpp

#include<iostream>
#include<stdio.h>
#include<math.h>
using namespace std;

int main()
{
	ios::sync_with_stdio(false);
	//freopen("input.txt", "r", stdin);

	int T;
	cin >> T;
	for(int tc = 0; tc < T; tc++)
	{
		double a,b,c,d;
		cin >> a >> b >> c >> d;

		double p = (a + b + c + d) / 2;
		double S = sqrt((p-a)*(p-b)*(p-c)*(p-d));

		printf("%.2lf\n", S);
	}
	return 0;
}