HDU 1071 The area

#include <stdio.h>

int main()
{
int t;
double x0,y0,x1,y1,x2,y2;
double k,b;
double a;
double s;
scanf("%d",&t);
while(t--)
{
scanf("%lf%lf%lf%lf%lf%lf",&x0,&y0,&x1,&y1,&x2,&y2);
k=(y2-y1)/(x2-x1);
b=y1-k*x1;
a=(y1-y0)/(x1-x0)/(x1-x0);
s=(a*x2*x2*x2/3-a*x0*x2*x2+(a*x0*x0+y0)*x2-a*x1*x1*x1/3+a*x0*x1*x1-(a*x0*x0+y0)*x1-k*x2*x2/2-b*x2+k*x1*x1/2+b*x1);
printf("%.2lf\n",s);
}
return 0;
}