#include<cstring>
#include<cstdio>
#include<cmath>
using namespace std;
double l,n,c,l1,hi,lo,pi,mid,f;
int main(void){

    while(true){
        scanf("%lf %lf %lf",&l,&n,&c);
        if(l<0 || n<0 ||c<0)break;
        l1=l+n*c*l;
        pi=3.1415926;mid=0;
        hi=pi/2;lo=0;mid=(hi+lo)/2;
        f=mid*l-sin(mid)*l1;
        while (abs(f)>1e-12)
        {         
            if (f>0) hi=mid; else lo=mid;
            mid=(hi+lo)/2;
            f=mid*l-sin(mid)*l1;
        }                
        printf("%.3lf\n",l1/mid/2*(1-cos(mid)));
    }
    return 0;
}

• 牛顿迭代吧，二次收敛，选择一个好的初值可以收敛得很快 (644) frkstyc 2005-04-15 14:57:36