zoj_3203 (三分）

Description

Compared to wildleopard‘s wealthiness, his brother mildleopard is rather poor. His house is narrow and he has only one light bulb in his house. Every night, he is wandering in his incommodious house, thinking of how to earn more money. One day, he found that the length of his shadow was changing from time to time while walking between the light bulb and the wall of his house. A sudden thought ran through his mind and he wanted to know the maximum length of his shadow.

Input

The first line of the input contains an integer T (T <= 100), indicating the number of cases.

Each test case contains three real numbers H, h and D in one line. H is the height of the light bulb while h is the height of mildleopard. D is distance between the light bulb and the wall. All numbers are in range from 10^-2 to 10³, both inclusive, and H - h >= 10^-2.

Output

For each test case, output the maximum length of mildleopard‘s shadow in one line, accurate up to three decimal places..

Sample Input

3
2 1 0.5
2 0.5 3
4 3 4

Sample Output

1.000
0.750
4.000

求影子长度的最大值，哦，最大值，那就是三分喽。



根据相似三角形边的关系，推导出公式影长：D-x+H-(H-h)*D/x；

#include<bits/stdc++.h>
using namespace std;
const double esp = 1e-10;
double H,h,D,L,R,mid,midd;

double f(double x){
	return D-x+H-(H-h)*D/x;
}

int main(){
	int T;
	scanf("%d",&T);
	while(T--){
		scanf("%lf %lf %lf",&H,&h,&D);
		mid = midd = 0.0;
		L=0.0; R=D;
		while(R-L>esp){
			mid=L+(R-L)/2.0;
			midd=mid+(R-mid)/2.0;
			if(f(mid)<f(midd))
				L=mid;
			else
				R=midd;
		}
		printf("%.3lf\n",f(L));
	}
	return 0;
}