题解 | 三角形面积

#include<bits/stdc++.h>
using namespace std;
int main(){
    int x1,x2,x3,y1,y2,y3;
    cin >> x1>> y1;
    cin >> x2 >> y2;
    cin >> x3 >> y3;
    double a = 0.5*abs((x2-x1)*(y3-y1) - (x3-x1)*(y2-y1));  // abs 不要忘了
    cout << fixed<<setprecision(2) << a <<endl;
    return 0; 
}