杭电acm the area

#include<iostream>
#include<cstdio>
using namespace std;
int main(){
int t;
scanf("%d",&t);
while(t--){
double x1,y1,x2,y2,x3,y3;
cin>>x1>>y1>>x2>>y2>>x3>>y3;
double k = (y3-y2)/(x3-x2);
double m = y2-k*x2;
double k1=(y2-y1)/((x2-x1)*(x2-x1));
double a = k1;
double b = -2*a*x1;
double c = a*x1*x1+y1;
double s =
a/3*(x3*x3*x3-x2*x2*x2)+
0.5*(b-k)*(x3*x3-x2*x2)+(c-m)*(x3-x2);
printf("%.2f\n",s);
}
}