POJ 4140:方程求解
看了模板之后也没有思路,于是直接看了题解:

#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
double search(double left,double right)
{
    double mid;
    double f;
    while(right-left>1e-11)
    {
        mid=left+(right-left)/2;
        f=mid*mid*mid-5*mid*mid+10*mid-80;
        if(f<0)
            left=mid;
        else
            right=mid;
    }
    return mid;
}
int main()
{
    printf("%.9lf\n",search(0.0,10.0));
    return 0;
} 

下面没有用模板，更好理解，但也是二分的思路:

#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
int main()
{
    double EPS=1e-11;
    double left=0,right=10,f;//f=f(mid)
    double mid=left+(right-left)/2;
    f=mid*mid*mid-5*mid*mid+10*mid-80;
    while(fabs(f)>EPS)
    {
        if(f>0) right=mid;
        else left=mid;
        mid=left+(right-left)/2;
        f=mid*mid*mid-5*mid*mid+10*mid-80;
    }

    printf("%.9lf\n",mid);
    return 0;
}