HDU 2899 Strange fuction

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

题解:

咳咳,不要说为什么可以看出是三分,打表大法好(其实我是用了函数绘制工具)......然后直接套板子即可

#include <algorithm>
#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
#include <cmath>
#define RG register
#define il inline
using namespace std;
const double eps=1e-6;
double y;
double f(double x){
    return 6*x*x*x*x*x*x*x+8*x*x*x*x*x*x+7*x*x*x+5*x*x-y*x;
}
void work()
{
    cin>>y;
    double l=0,r=100,lmid,rmid;
    while(l+eps<r){
        lmid=l+(r-l)/3;rmid=r-(r-l)/3;
        if(f(lmid)>f(rmid))l=lmid;
        else r=rmid;
    }
    printf("%.4lf
",f(l));
}

int main()
{
    int T;cin>>T;
    while(T--)
        work();
    return 0;
}