uva 12300 - Smallest Regular Polygon

题意：给定两个点A和B，求包含这两个点的面积最小的正 n（已知）边形。

 

#include<iostream>

#include<iomanip>

#include<cmath>

#define pi 2.0*asin(1.0)

#define sqr(a) ((a)*(a))



using namespace std;



int main()

{

    int n;

    double x1,x2,y1,y2,d,thy,s;

    while(cin>>x1>>y1>>x2>>y2>>n && x1+x2+y1+y2+n)

    {

        d=sqrt(sqr(x1-x2)+sqr(y1-y2));

        thy=pi-2*pi/n;

        if(n%2)

            s=n*sqr(d*cos((thy+pi)/4))*tan(thy/2);

        else

            s=n*sqr(d/2)*sin(thy)/2;

        cout<<fixed<<setprecision(6)<<s<<endl;

    }

    return 0;

}