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poj 1905Expanding Rods

 1 /* 2   二分 + 几何 3   弧长L, 圆半径R, 弧度 q, L=R*q; 4   二分: 弧度(0~PI) 或者 高度(L/2~L)  5 */ 6 #include<cstdio>  7 #include<iostream> 8 #include<cmath> 9 using namespace std;10 const double PI = acos(-1.0);11 double L, L1, T, C, R, Q;12 13 int main(){14    15    while(scanf("%lf%lf%lf", &L, &T, &C) && (L!=-1 || T!=-1 || C!=-1)){16       L1 = (1+T*C)*L;17       double ld=0.0, rd=PI, tmp;18       Q = (ld+rd)/2; 19       R = L/2/sin(Q);20       while(fabs(tmp = R*2*Q-L1)>1e-8){21          if(tmp>0) rd=Q;22          else ld=Q;23          Q=(ld+rd)/2;24          R = L/2/sin(Q);25       }26       printf("%.3lf\n", R-sqrt(R*R - (L/2)*(L/2)));27    } 28    return 0;29 }