HDU 1071 The area (数学定积分)

#include <cstdio>
#include <iostream>

using namespace std;

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