超简单题解（正常非打表）

#include<bits/stdc++.h>
#pragma GCC optimize(3)
#define IOS ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
using namespace std;
const int N=1e6+10;
const int INF=0x3f3f3f3f;
double area;
double x,y,x2,y2,x3,y3;
void calculate_triangle_area()
{
	area=0.5*abs((x*(y2-y3)+x2*(y3-y)+x3*(y - y2)));//精华所在
}
int main()
{
	IOS;
	cin>>x>>y>>x2>>y2>>x3>>y3;
	calculate_triangle_area();
	cout<<fixed<<setprecision(2)<<area;
    return 0;
}