POJ 1905 Expanding Rods （求直杆弯曲拱起的高度）（二分法，相交弦定理）

Description

When a thin rod of length L is heated n degrees, it expands to a new length L' = (1+n*C)*L, where C is the coefficient of heat expansion.

When a thin rod is mounted on two solid walls and then heated, it expands and takes the shape of a circular segment, the original rod being the chord of the segment.

Your task is to compute the distance by which the center of the rod is displaced. That means you have to calculate h as in the picture.

Input

Input starts with an integer T (≤ 20), denoting the number of test cases.

Each case contains three non-negative real numbers: the initial length of the rod in millimeters L, the temperature change in degrees n and the coefficient of heat expansion of the material C. Input data guarantee that no rod expands by more than one half of its original length. All the numbers will be between 0 and 1000 and there can be at most 5 digits after the decimal point.

Output

For each case, print the case number and the displacement of the center of the rod in single line. Errors less than 10^-6 will be ignored.

Sample Input

3

1000 100 0.0001

150 10 0.00006

10 0 0.001

Sample Output

Case 1: 61.3289915

Case 2: 2.2502024857

Case 3: 0

若圆内任意弦AB、弦CD交于点P，则PA·PB=PC·PD（相交弦定理）

sinB=L/R   B=asin(L/R)   反三角函数。

 #include<cstdio>
 #include<cmath>
 int main()
 {
     int t;
     scanf("%d",&t);
     int num=;
     while(t--)
     {
         double l,n,c,L,le,ri,r,mid;
         scanf("%lf %lf %lf",&l,&n,&c);
         L=(+n*c)*l;
         le=;
         ri=l/;
         while(ri-le>1e-)
         {
             mid=(le+ri)/;
             r=l*l//mid+mid/;
             if(r**(asin(l//r))<L)
             {
                 le=mid;
             }
             else
             {
                 ri=mid;
             }
         }
         printf("Case %d: ",++num);
         printf("%.6f\n",le);
     }
 }