#include <stdio.h>
#include <math.h>
/* halley.c : 1999 5 2 */
double halley(f, f1, f2, x0, itr, tol)
  double (*f)(), (*f1)(), (*f2)(), x0, tol;
  int itr;
{
  double x;
  int i;
  for(i=1; i<=itr; i++){
    x=x0-f(x0)/(f1(x0)-f(x0)*f2(x0)/(2.0*f1(x0)));
    if (fabs(x-x0)<=tol) break;
    x0=x;
  }
/*  printf("%d\n",i); */
  return x;
}
double f(double x) { return x*x-2.0; }
double f1(double x) { return 2.0*x; }
double f2(double x) { return 2.0; }
/* main */
main(){
  double x;
  x=halley(f,f1,f2,2.0,10,0.0001);
  printf("•½•û�ª‚Í %f\n", x);
}