C++ Newton Method

Implementation of Newton Method written in C++.

IN
-3
0.0000001
OUT
X: -3 f(x): 2
X: -2.5 f(x): 0.25
X: -2.41667 f(x): 0.00694444
X: -2.41422 f(x): 6.0073e-06

// ? 2018 TheFlyingKeyboard and released under MIT License
// theflyingkeyboard.net

#include <iostream>
#include <math.h>

using namespace std;
static double function(double x);
static double functionDerivative(double x);

int main() {
  double prevX; 
  double x;
  double precision;

  cout << "Enter initial guess: ";
  cin >> x;

  prevX = x;

  cout << "Enter precision of method: ";
  cin >> precision;

  while (abs(function(x)) > precision) {
    cout << "X: " << x << " f(x): " << function(x) << endl;

    x = prevX - (function(prevX) / functionDerivative(prevX));
    prevX = x;
  }

  int a;
  cin >> a; //Wait before exiting

  return 0;
}

static double function(double x) //x^2 + 2x -1
{
  return x * (x + 2) - 1;
}

static double functionDerivative(double x)
{
  return 2 * x + 2;
}