三角形有向面積*2

#include<stdio.h>

double area2 (double x0, double y0, double x1, double y1, double x2, double y2){
	return (x0*y1 + x2*y0 + x1*y2 - x2*y1 - x0*y2 - x1*y0) / 2;
}

int main () {
	
	printf("%lf", area2(0.0, 0.0, 0.0, 1.0, 1.0, 1.0));
	
	return 0;
}