Codeforces 1354 C2. Not So Simple Polygon Embedding

$n$ 是奇数的情况其实本质上就是把 $n$

由对称性可得，当转过的角度等于 $\frac{1}{4}$

AC代码：

const double PI = 3.1415926535898;
int n, m;
int main()
{
  int t;
  sd(t);
  while (t--)
  {
    sd(n);
    double ang = 360.0 / (2 * n);
    ang /= 2.0;
    double ans = 0.0;
    ans = 0.5 / sin(ang / 180.0 * PI) * cos(0.5 * ang / 180.0 * PI) * 2;
    printf("%.9lf\n", ans);
  }
  return 0;
}