C :

#include <stdio.h>
#include <math.h>
int main()
{
  double a, b, x, y;
  scanf("%lf", &x);
  y = x + 1;
  while(fabs(x - y) >= 1e-6)
  {
    y = x;
    a = 2 * pow(x, 3) - 4 * x * x + 3 * x -6;
    b = 6 * x * x - 8 * x + 3;
    x = x - a / b;
  }
  printf("%.6lf\n", y);
  return 0;
}

C++ :

#include<stdio.h>
#include <math.h>
int main()
{
  float x,x0,f,f1; 
  scanf("%d",&x); 
  do{
    x0=x;    
    f=2*x0*x0*x0-4*x0*x0+3*x0-6;  
    f1=6*x0*x0-8*x0+3;  
    x=x0-f/f1; }
  while(fabs(x-x0)>=1e-5); 
  printf ("%f\n",x); 
}