已知圆心（0,0）圆周上的一点，求圆周上另外两点使得三点构成等边三角形。

懒得推公式，直接用模板2圆（r1=dist，r2=sqrt(3)*dist）相交水过

#include<cstdio>

#include<iostream>

#include<cmath>

#include<algorithm>

#include<iterator>

using namespace std;

#define eps 1e-6

typedef long long ll;

inline double sqr(double x)

{

    return x*x;

}

int gcd(int a,int b)

{

    return b==0?a:gcd(b,a%b);

}

int sig(double x)

{

    if(fabs(x)<eps) return 0;

    if(x>0) return 1;

    return -1;

}

struct point

{

    double x,y;

    point(){};

    point(double a,double b):x(a),y(b){}

    void input()

    {

        scanf("%lf%lf",&x,&y);

    }

    friend point operator + (const point &a,const point &b)

    {

        return point(a.x+b.x,a.y+b.y);

    }

    friend point operator - (const point &a,const point &b)

    {

        return point(a.x-b.x,a.y-b.y);

    }

    friend bool operator == (const point &a,const point &b)

    {

        return sig(a.x-b.x)==0 && sig(a.y-b.y)==0;

    }

    friend point operator * (const point &a,const double &b)

    {

        return point(a.x*b,a.y*b);

    }

    friend point operator * (const double &a,const point &b)

    {

        return point(a*b.x,a*b.y);

    }

    friend point operator / (const point &a,const double &b)

    {

        return point(a.x/b,a.y/b);

    }

    double norm()

    {

        return sqrt(sqr(x)+sqr(y));

    }

}a,b;

double det(const point &a,const point &b)

{

    return a.x*b.y-a.y*b.x;

}

double dot(const point &a,const point &b)

{

    return a.x*b.x+a.y*b.y;

}

double dist(const point &a,const point &b)

{

    return (a-b).norm();

}

point rotate_point(const point &p,double A)

{

    double tx=p.x,ty=p.y;

    return point(tx*cos(A)-ty*sin(A),tx*sin(A)+ty*cos(A));

}

point rotate(const point &p,double cost,double sint)

{

    double x=p.x,y=p.y;

    return point(x*cost-y*sint,x*sint+y*cost);

}

pair<point,point> crosspoint(point ap,double ar,point bp,double br)

{

    double d=(ap-bp).norm();

    double cost=(ar*ar+d*d-br*br)/(2*ar*d);

    double sint=sqrt(1.0-cost*cost);

    point v=(bp-ap)/(bp-ap).norm()*ar;

    return make_pair(ap+rotate(v,cost,-sint),ap+rotate(v,cost,sint));

}

int main()

{

    int cas;b.x=0;b.y=0;

    scanf("%d",&cas);

    while(cas--)

    {

        a.input();

        double r=dist(a,b);

        pair<point,point> ans=crosspoint(b,r,a,sqrt(3.0)*r);

        double x1=ans.first.x,y1=ans.first.y,x2=ans.second.x,y2=ans.second.y;

        if(y1<y2||y1==y2&&x1<x2) printf("%.3lf %.3lf %.3lf %.3lf\n",x1,y1,x2,y2);

        else printf("%.3lf %.3lf %.3lf %.3lf\n",x2,y2,x1,y1);

    }

    return 0;

}