Strange fuction HDU 2899 "two minutes"

Problem Descriptionnow, 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.
Inputthe first line of the input contains an integer T (1<=t<=100) which means the number of test cases. Then T-lines follow, each of the line have only one real numbers y. (0 < y <1e10)
Outputjust the minimum value (accurate up to 4 decimal places) while X is between 0 and 100.
Sample Input

2100200

Sample Output

-74.4291-178.8534

#include <stdio.h> #include <math.h>int y;double fun1 (double x) {    return 42*pow (x,6) + 48*pow (x,5) + 21*x* x + 10*x-y;} Double fun2 (double x) {    return 6*pow (x,7) + 8*pow (x,6) + 7*x*x*x + 5*x*x-y*x;} int main () {    int T;    scanf ("%d", &t);    while (t--)    {        scanf ("%d", &y);        Double Left=0,right=100,middle;        while (right-left>=1e-10)        {            middle= (left+right)/2;            if (fun1 (middle) >0) Right=middle;            else left=middle;        }        printf ("%.4lf\n", fun2 (left));    }    return 0;}

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Strange fuction HDU 2899 "two minutes"