还没学过导数，不会做……

#include 
     
      #include 
      
       using namespace std;//先求导函数,可知f'(x)=g'(x)+y,g'(x)为递增函数,//1)若导函数最大值小于0,即g'(100)+y<0.则原函数在区间内单调递减.最小值为f(100).//2)若导函数最小值大于0,即g'(0)=y>0,则原函数在区间内单调递增,最小值为f(0).//3)若导函数有正有负,因导函数单调递增,所以必然从负值开始穿过x轴,导函数由负变正,原函数先减后增,其0点即原函数的最小值点.//(或求二阶导数,在区间内,f''(x)>0,则原函数为凹函数,有最小值点.否则,为凸函数,有最大值点)double f(double x,int y){    return 6 * pow(x,7) + 8 * pow(x,6) + 7 * pow(x,3) + 5 * pow(x,2) - y * x; }double g(double x,int y){    return 42 * pow(x,6) + 48 * pow(x,5) + 21 * pow(x,2) + 10 * x - y;}int main(int argc, const char *argv[]){    int T;    cin>>T;    while(T--)    {        int Y;        cin>>Y;        if(g(100.0,Y)<0) printf("%.4lf\n",f(100,Y));        else if(g(0.0,Y)>0) printf("%.4lf\n",f(0,Y));        else        {            double low = 0 , heigh = 100.0;            double mid ;            while (heigh-low>1e-8)            {                mid = (low+heigh)/2;                if(g(mid,Y)>0)                {                    heigh = mid;                }else                {                    low = mid;                }            }            printf("%.4lf\n",f(mid,Y));        }    }    return 0;}