HDU 1071 The area 平面几何

题目大意：   如图，给定途中p1,p2,p3的点的 坐标，求阴影部分的面积。           

解题报告：分别解出抛物线和直线的方程，然后对(a*x^2+b*x+c)-kx-m积分，范围是p2到p3，公式看代码。

#include<cstdio>
#include<cmath>
int main( ) {
    int T;
    double x1,y1,x2,y2,x3,y3,a,b,c,k,m;
    while(scanf("%d",&T)!=EOF) {
        while(T--) {
            scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3);
            a=b=c=k=m=0;
            if(x3!=x2&&x1!=x2)
            b=1.0*(((x2*x2-x1*x1)/(x3*x3-x2*x2))*(y3-y2)-y2+y1)/((x2*x2-x1*x1)/(x3+x2)-x2+x1);
            if(x1!=x2)
            a=1.0*(y2-y1-b*(x2-x1))/(x2*x2-x1*x1);
            c=1.0*y1-a*x1*x1-b*x1;
            if(x3!=x2)
            k=1.0*(y3-y2)/(x3-x2);
            m=1.0*y2-k*x2;
            
            double sum1=(a/3.0)*x2*x2*x2+((b-k)/2.0)*x2*x2+(c-m)*x2;
            double sum2=(a/3.0)*x3*x3*x3+((b-k)/2.0)*x3*x3+(c-m)*x3;
            printf("%.2lf\n",sum2-sum1);
        } 
    }
    return 0;
}