一根细棒升温时会变长，在两面墙中间，会变成一个弓形。
给出变长后的长度，求新的细棒中心与没伸长时的中心的距离。
简单的数学推导后就可以二分答案了，一开始没完全掌握二分的姿势，wa了好多。而且poj double输出要用%f，用%lf就wa了。
#include <cstdio>
#include <cmath>
#include <algorithm> using namespace std; const double eps = 1e-;
double n,c,L; double func(double x)
{
//if(fabs(x-0) < eps) return ;
double r = (x*x+L*L/4.0)/(*x);
return *r*asin(L/(2.0*r));
} int main()
{
while(scanf("%lf%lf%lf",&L,&n,&c))
{
if(L< && n< && c<)
break; double low = 0.0,high = 0.5*L;
double mid = (low+high)/2.0;
double s = (+n*c)*L;
double ans = ; while(high-low>eps)
{
//printf("%lf %lf %lf\n",low,mid,high);
//printf("%lf %lf %lf\n",func(low),func(mid),func(high)); if(func(mid) < s)
low = mid;
else
high = mid; mid = (low+high)/2.0;
}
//printf("%f %f\n",mid,L);
printf("%.3f\n",mid);
}
}