埃特金算法

#include <iostream>
#include <math.h>
using namespace std;

double f(double a){

return exp(-a);
}

int main(){

double x0,e,x1,x2;
int k,N;

cin>>x0>>e>>N;
k=0;
x2=x0;
do{
k=k+1;
x0=x2;
x1=f(x0);

x2=f(x1);

x2=x2-(x2-x1)*(x2-x1)/(x2-2.0*x1+x0);

if(fabs(x2-x0)<e)
{
cout<<x2<<endl;
exit(0);