Ошибка преобразования

#include "stdafx.h"
#include <iostream>
#include <cmath>
#include <Windows.h>
using namespace std;
 
double f1(double x)
{
    return x*x*x-x*x*3+9*x+2;
}
double d1f1(double x)
{
    return 3*x*(x-2)+9;
}
double d2f1(double x)
{
    return 6*x-6;
}
 
double f2(double x)
{
    return log10(x)-(7/(2*x+6));
}
double d1f2(double x,double e)
{
    return (1/(log10(e)*x))+(14/pow(2*x+6,2));
}
double d2f2(double x,double  e)
{
    return -log10(e)*pow(log10(e),-2)*pow(x,-2)-7*(x+3)*pow(x+3,-4);
}
 
 
double kasat(double a, double b, double epsilon, double (*f)(double), double (*df)(double), double (*d2f)(double))
{
    double x,xn;
    if (f(a)*d2f(a)>0) x=a;
    else x=b;
    xn = x - f(x)/df(x);
    while (abs(xn-x)>epsilon)
    {
        x = xn;
        xn = x - f(x)/df(x);
    }
    return x;
}
 
 
int main()
{
    setlocale( LC_ALL,"Russian");
    double a,b,epsilon, x1,x2;
    cout << "Метод касательних" << endl;
    cout << "x*x*x-x*x*3+9*x+2" << endl;
    cout << "Перша границя "; cin >> a; cout << "Друга границя "; cin >> b; cout << " епселент "; cin>> epsilon;
    x1 = kasat(a, b, epsilon, f1, d1f1, d2f1);
    cout << "Знайденний корiнь = " << x1 << endl;
    cout << "log(x)-(7/(2*x+6))" << endl;
    cout << "Перша границя "; cin >> a; cout << "Друга границя "; cin >> b; cout << " епселент "; cin>> epsilon;
    x2 = kasat(a, b, epsilon, f2, d1f2, d2f2);
    cout << "Знайденний корiнь = " << x2 << endl;
    system("pause");
    return 0;
}

double d1f2(double x,double e)
//...
double d2f2(double x,double  e)
//...
double (*df)(double), double (*d2f)(double)
//...
kasat(a, b, epsilon, f1, d1f1, d2f1);