题目链接：http://lightoj.com/volume_showproblem.php?

problem=1043

题意：一个三角形ABC，DE//BC。已知三角形ADE和四边形BDEC的面积的比，求AD的长度。

解法：二分AD边就可以

代码：

#include <stdio.h>

#include <ctime>

#include <math.h>

#include <limits.h>

#include <complex>

#include <string>

#include <functional>

#include <iterator>

#include <algorithm>

#include <vector>

#include <stack>

#include <queue>

#include <set>

#include <map>

#include <list>

#include <bitset>

#include <sstream>

#include <iomanip>

#include <fstream>

#include <iostream>

#include <ctime>

#include <cmath>

#include <cstring>

#include <cstdio>

#include <time.h>

#include <ctype.h>

#include <string.h>

#include <assert.h>

using namespace std;

int main()

{

    int t; int cases = 1;

    double a, b, c, ratio;

    scanf("%d",&t);

    while (t--)

    {

        cin >> a >> b >> c >> ratio;

        double s = a*b;

        double ans;

        ratio = ratio / (ratio + 1.0);

        double left = 0, right = a;

        double mid;

        while (left + 0.000000001<= right)

        {

            mid = (left + right) / 2.0;

            ans = mid * b * (mid / a);

            ans /= s;

            if (ans >= ratio) right = mid;

            else left = mid;

        }

        printf("Case %d: ", cases++);

        printf("%.9lf\n", right);

    }

    return 0;

}