POJ 1905 Expanding Rods 二分答案几何

题目：http://poj.org/problem?id=1905

恶心死了，POJ的输出一会要lf，一会要f，而且精度1e-13才过，1e-12都不行，错了一万遍终于对了。

 #include <stdio.h>
 #include <math.h>

 int main()
 {
     double l, n, c, r;
     while(scanf("%lf %lf %lf", &l, &n, &c) != EOF)
     {
         if(l <  && n <  && c < )break;
         double arc = ( + n*c) * l;
         double low = , high = acos(-1.0) / ;
         while(high-low > 1e-)
         {
             double mid = (high+low) / ;
             r = l/ / sin(mid);
             if(r * mid < arc / )
             {
                 low = mid;
             }
             else
             {
                 high = mid;
             }
         }
         printf("%.3lf\n", r-r*cos(low));
     }
     return ;
 }