在区间(0,100)，二次导数恒大于0，f(x)有极小值，用一次导数求极小值点；

#include<math.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
const double eps=1e-6;
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;
}
double fpi(double x,double y)
{
    return 42*pow(x,6)+48*pow(x,5)+21*pow(x,2)+10*x-y;
}
double slove(double y)
{
    double left=0.0,right=100.0,mid;
    while(right-left>eps)
    {
        mid=(left+right)/2;
        if(fpi(mid,y)<0.0)
            left=mid;
        else
            right=mid;
    }
    return mid;
}
int main(void)
{
    int t;
    double y;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%lf",&y);
        printf("%.4f\n",f(slove(y),y));
    }
    return 0;
}

hdu2899 Strange fuction