HDU2899 Strange fuction（简单三分）

Problem Description

            Now, here is a fuction: F(x) = 6 * x^7+8*x^6+7*x^3+5*x^2-y*x (0 <= x <=100)
            Can you find the minimum value when x is between 0 and 100.

Input

            The first line of the input contains an integer T(1<=T<=100) which means the number of test cases.

            Then T lines follow, each line has only one real numbers Y.(0 < Y <1e10)

Output

            Just the minimum value (accurate up to 4 decimal places),when x is between 0 and 100.

Sample Input

       2 100 200

Sample Output

       -74.4291 -178.8534

#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#include <queue>
#include <cmath>
#include <algorithm>
using namespace std;
#define eps 1e-9
double f(double x,double y)
{
    return 6*pow(x,7)+8*pow(x,6)+7*pow(x,3)+5*pow(x,2)-y*x;
}
int main()
{
    //freopen("in.txt","r",stdin);
    int t;
    double y;
    double mid,midmid;
    double left,right;
    cin>>t;
    while(t--)
    {
        cin>>y;
        left=0;right=100;;
        while(left+eps<right)
        {
              mid=(left+right)/2;
              midmid=(mid+right)/2;
              if(f(mid,y)<f(midmid,y))
              right=midmid;
              else
              left=mid;
        }
        printf("%.4lf
",f(mid,y));
    }
    return 0;
}