hdu2899 简单数学+二分+三分

#include<iostream>
#include<cmath>
#include<cstdio>
using namespace std;
const double b=1e-6;
double f(double x)
{
return 42*pow(x,6)+48*pow(x,5)+21*pow(x,2)+10*x;
}
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;
}
int main()
{
int T;
double x,y,l,r;
cin>>T;
while(T--)
{
cin>>y;
if(f(100)<=y)
{
printf("%.4lf\n",F(100,y));
}
else
{
l=0;r=100;
while(r-l>b)
{
if(f((r+l)/2)>y) r=(r+l)/2;
else l=(r+l)/2;
}
printf("%.4lf\n",F(l,y));
}
}
return 0;
}

#include<iostream>
#include<cmath>
#include<cstdio>
using namespace std;
const double b=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;
}
int main()
{
int T;
double l,r,lm,rm,y;
cin>>T;
while(T--)
{
cin>>y;
l=0;r=100;
while(r-l>b)
{
lm=(2*l+r)/3;
rm=(l+2*r)/3;
if(F(lm,y)>F(rm,y)) l=lm;
else r=rm;
}
printf("%.4lf\n",F(l,y));
}
return 0;
}