HDU 2199 Can you solve this equation?

题解：二分求解

#include <cstdio>

#include <cmath>

using namespace std;



double f(double x)

{

    return(8*pow(x,4)+7*pow(x,3)+2*pow(x,2)+3*x+6);

}



int main()

{

    int t;

    double l,r,mid,yl,yr,y,y1;

    scanf("%d", &t);

    while(t--)

    {

        l=0;

        r=100;        

        scanf("%lf",&y1);   

        yl=f(l)-y1;

        yr=f(r)-y1;

        if (yl>0||yr<0)

            printf("No solution!\n");

        else{

            while (fabs(l-r)>=0.000000001)

            {

                mid=(l+r)/2;

                y=f(mid)-y1;

                if (y>=0) r=mid;

                else l=mid;

            }

            printf("%0.4lf\n",mid);

        }

    }

    return 0;

}