hoj1700

利用点积和叉积列方程

(x0,y0)X (x1,y1) = sin(120)*R^2     (r为圆的半径)
(x0,y0) * (x1,y1) = cos(120)*R^2
结果为：
x1=b*x0-a*y0;
a=sin120;
y1=b*y0+a*x0;   
b=cos120;

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
using namespace std;

#define eps 0.0005

void make(double x0, double y0, double &x1, double &y1)
{
    double a, b;

    a = sqrt(3.0) / 2.0;
    b = -1 / 2.0;
    x1 = x0 * b - y0 * a;
    y1 = y0 * b + x0 * a;
}

int main()
{
    //freopen("D:\\t.txt", "r", stdin);
    int t;
    scanf("%d", &t);
    while (t--)
    {
        double x0, y0, x1, y1, x2, y2;
        scanf("%lf%lf", &x0, &y0);
        make(x0, y0, x1, y1);
        make(x1, y1, x2, y2);
        if (y1 < y2 || abs(y1 - y2) < eps && x1 - x2 < eps)
        {
            swap(y1, y2);
            swap(x1, x2);
        }
        printf("%.3f %.3f %.3f %.3f\n", x2, y2, x1, y1);
    }
    return 0;
}