测试点2WA，以下是代码：

#include<bits/stdc++.h>
using namespace std;

int main() {
	
	double x1, y1, x2, y2, x3, y3;
	cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
	cout << fixed << setprecision(2);
	cout << abs((x1 - x3) * (y1 - y3) - (x2 - x3) * (y2 - y3) / 2);
	
	return 0;
}