метод парабол

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<string>
#include<alg.h>

using namespace std;
const double EPS = 1e-4;
const double DELTA = 1e-5;
const int INF = 1e8 + 13;
const double goldenRatio1 = (3 - sqrt(5)) / 2; // "Золотое" число
const double goldenRatio2 = (sqrt(5) - 1) / 2; // "Золотое" число

double func(double x)
{
    return 2. * x*x - 6 * x - 3;
}

pair<double, double> solve()
{

    double h = 0.001;
    double x = -1;

    if (x == 0)
        x += 0.1;
    while ((func(x + h) - 2 * func(x) + func(x - h)) / (h*h) <= 0)
        x += 0.1;
    double x1;
    x1 = x - 0.5*h*(func(x + h) - func(x - h)) / (func(x + h) - 2 * func(x) + func(x - h));
    while (fabs(x1 - x) > EPS)
    {
        x = x1;
        x1 = x - 0.5*h*(func(x + h) - func(x - h)) / (func(x + h) - 2 * func(x) + func(x - h));
    }

    return { x1, func(x1) };
}

int main()
{
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);

    pair<double, double> ans = solve();
    cout << "min = " << ans.first << "\nwith x =  " << ans.second << endl;

}