已知3点坐标O(1)求三角形面积

//(xa,ya),(xb,yb),(xc,yc)为三点坐标

#include<bits/stdc++.h>

using namespace std;

int main(){

double xa,xb,xc,ya,yb,yc,area;

    cin>>xa>>ya>>xb>>yb>>xc>>yc;

    area=0.5*fabs(xa*yb+xb*yc+xc*ya-xa*yc-xc*yb-xb*ya);

    printf("%.2lf",area);

return 0;

}