Strange fuction hdu 2899

Strange fuction

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 4803    Accepted Submission(s): 3428

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

 

Author

Redow

题意：给一式子，还有变量范,0-100，让求最小值，。导数等于0时，二分查找导数等于0的时候的x~我怎么把二分这么重要的查找方式给忘了呢，当时还在想这x是实数怎么找啊~蠢到猪

#include<iostream>
#include<cstdio>
#include<cstring>

using namespace std;

double y;

double slove(double x)
{
    return 42.0*x*x*x*x*x*x+48.0*x*x*x*x*x+21.0*x*x+10.0*x-y;
}
double get(double x)
{
    return 6.0*x*x*x*x*x*x*x+8.0*x*x*x*x*x*x+7.0*x*x*x+5.0*x*x-y*x;
}

int main()
{
    int t;
    scanf("%d", &t);
    while(t--)
    {
        scanf("%lf", &y);
        double l = 0.0, r = 100.0;
        while(r-l >= 1e-6)  //  double 比较，不能写成 r > l 
        {
            double mid = (l+r)/2;
            if(slove(mid) > 0)
                r = mid;
            else
                l = mid;
        }
        printf("%.4f
", get(l));
    }
    return 0;
}

蠢成猪肿么办~