HDOJ1071

The area

拿到题的第一想法，又是一道水题，知道P1、P2、P3三点的坐标，就能够确定抛物线的公式。确定抛物线的公式就能够进行积分，然后就没有然后了。纯粹的数学题。

#include<iostream>
using namespace std;
int main()
{
	double x1,y1,x2,y2,x3,y3,a,b,c,s;
	int n;
	while(cin>>n&&n)
	{
		for(int i=0;i<n;i++)
		{
			cin>>x1>>y1;
			cin>>x2>>y2;
			cin>>x3>>y3;
			a = ((y2-y1)*(x3-x2)/(x2-x1)-(y3-y2))/((x2*x2-x1*x1)*(x3-x2)/(x2-x1)-(x3*x3-x2*x2));
            b = ((y2-y1)-a*(x2*x2-x1*x1))/(x2-x1);
            c = y1-a*x1*x1-b*x1;
            s = (a/3*x3*x3*x3+b/2*x3*x3+c*x3)-(a/3*x2*x2*x2+b*x2*x2/2+c*x2)-(y3+y2)*(x3-x2)/2;
            printf("%.2lf\n",s);
		}
	}
	return 0;
}