1034：计算三角形面积

#include
#include
using namespace std;
double bianchang (double a1,double a2,double b1,double b2)
{
    return sqrt((a1-b1)*(a1-b1)+(a2-b2)*(a2-b2));
}
int main ()
{
    double x1, y1, x2, y2, x3, y3;
    scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3);
    double A=bianchang(x1,y1,x2,y2);
    double B=bianchang(x2,y2,x3,y3);
    double C=bianchang(x3,y3,x1,y1);
    double q=(A+B+C)/2;
    double S=sqrt(q*(q-A)*(q-B)*(q-C));
    printf("%.2lf",S);
    return 0;
}