#include <stdio.h>
#include <math.h>
#include "prog04header.h"

/* prog04_4.c */
double CalcArea( Triangle triangle ){
  XY p1, p2;
  double crsProduct, area;

  p1.x = triangle.vertex[1].x - triangle.vertex[0].x;
  p1.y = triangle.vertex[1].y - triangle.vertex[0].y;
  p2.x = triangle.vertex[2].x - triangle.vertex[0].x;
  p2.y = triangle.vertex[2].y - triangle.vertex[0].y;
  
  crsProduct = p1.x * p2.y - p1.y * p2.x;

  area = fabs( crsProduct ) / 2.0;  
  return area;
}