第四届省赛A题

http://acm.upc.edu.cn/problem.php?id=2217

给定逆时针序三角形两点坐标，求第三点坐标

我会告诉你我用画图画的么- -

#include <iostream>
#include <cmath>
#include <stdio.h>

using namespace std;

#define pi acos(-1.0)

int main()
{
    int n;
    cin>>n;
    while(n--)
    {
        double x1, y1, x2, y2;
        cin>>x2>>y2>>x1>>y1;
        
        double alpha = atan2((y1-y2),(x1-x2));
        double l = sqrt((y1-y2)*(y1-y2)+(x1-x2)*(x1-x2));
        double x3=x2+l*cos(alpha+pi/3);
        double y3=y2+l*sin(alpha+pi/3);
        
        printf("(%.2f,%.2f)\n",x3,y3);
    }
}