三分求点到二次函数最小值

#include <cstdio>
#include <cmath>
const double eps=0.00000001;
double getf(double a,double b,double c,double x,double x0,double y0)
{
double t=a*x*x+b*x+c;
return sqrt((x0-x)*(x0-x)+(y0-t)*(y0-t));
}
int main()
{
double a,b,c,x,y;
scanf("%lf%lf%lf%lf%lf",&a,&b,&c,&x,&y);
double l=-200,h=200;
while(h-l>=eps){
double lm=(l+h)/2,rm=(lm+h)/2;
double tl=getf(a,b,c,lm,x,y),tr=getf(a,b,c,rm,x,y);
if(tl>tr) l=lm;
else h=rm;
}
printf("%.3lf\n",getf(a,b,c,l,x,y));
return 0;
}