C :

#include<stdio.h>
#include<math.h>
float solve(float a,float b,float c,float d,float x);

int main()
{
	float a,b,c,d,k;
	scanf("%f%f%f%f%f",&a,&b,&c,&d,&k);
	printf("%.4f\n",solve(a,b,c,d,k));
	return 0;
}

float solve(float a,float b,float c,float d,float x)
{
	while(fabs(a*x*x*x+b*x*x+c*x+d)>0.000001)
	{
		x=x-(a*x*x*x+b*x*x+c*x+d)/(3*a*x*x+2*b*x+c);
	}
		return x;
}

C++ :

#include <stdio.h>
#include <math.h>
int main() {
	float solve(float a, float b, float c, float d, float x);
	float a, b, c, d, k;
	scanf("%f%f%f%f%f", &a, &b, &c, &d, &k);
	printf("%.4f\n", solve(a, b, c, d, k));
	return 0;
}
float solve(float a, float b, float c, float d, float x) {
	while (fabs(a * x * x * x + b * x * x + c * x + d) > 1e-6) {
		x = x - (a * x * x * x + b * x * x + c * x + d) / (3 * a * x * x + 2 * b * x + 3 * c);
	}
	return x;
}

Pascal :

var 
  a,b,c,d,k:double; //全局

function solve():double;
var x:double;
begin
  x:=k;
  while( abs(a*x*x*x+b*x*x+c*x+d)>1e-6 ) do
    x:=x-(a*x*x*x+b*x*x+c*x+d)/(3*a*x*x+2*b*x+3*c);
  solve:=x;
end;

begin
  readln(a,b,c,d,k);
  writeln( solve():0:4 );
end.