HDU 1071 The area

 1 #include<stdio.h>
 2 int main()
 3 {
 4     int T;
 5     double x1,x2,x3,y1,y2,y3,a,b,c,k,h,ans;
 6     scanf("%d",&T);
 7     while(T--)
 8     {
 9         scanf("%lf%lf",&x1,&y1);
10         scanf("%lf%lf",&x2,&y2);
11         scanf("%lf%lf",&x3,&y3);
12         k=(y3-y2)/(x3-x2);
13         h=y3-k*x3;
14         a=(y2-y1)/( (x2*x2-x1*x1)-2*x1*(x2-x1) );
15         b=-2*a*x1;
16         c=y1-a*x1*x1-b*x1;
17         ans=(a*x3*x3*x3/3+(b-k)*x3*x3/2+(c-h)*x3)-(a*x2*x2*x2/3+(b-k)*x2*x2/2+(c-h)*x2);
18         printf("%.2lf\n",ans);
19     }
20     return 0;
21  }