static double metoda_stycznych(double XY, String xy, double epsilon) {
        double a = -100, b = 100;
        double x, y;
        int iter = 0;
        ArrayList<Double> xn = new ArrayList<>();
        xn.add(100.0);
        ArrayList<Double> yn = new ArrayList<>();
        yn.add(100.0);


        if(xy == "x") {
            y = XY;
            x = 0;
            if((pochodna_x(a, y) >= 0 && pochodna_x3(b, y) >= 0) || (pochodna_x(a, y) < 0 && pochodna_x(b, y) < 0)) {
                xn.add(a);
            } else {
                xn.add(b);
            }

            while(Math.abs(pochodna_x(xn.get(iter+1), y)) >= epsilon || Math.abs(xn.get(iter+1) - xn.get(iter)) >= epsilon) {
                xn.add(xn.get(iter) - (pochodna_x(xn.get(iter), y) / pochodna_x2(xn.get(iter), y)));

                System.out.println("xn1 = " + xn.get(iter));
                iter++;
            }
        }

        if(xy == "y") {
            x = XY;
            y = 0;
            if((pochodna_y(a, y) >= 0 && pochodna_y3(b, y) >= 0) || (pochodna_y(a, y) < 0 && pochodna_y3(b, y) < 0)) {
                yn.add(a);
            } else {
                yn.add(b);
            }

            while(Math.abs(pochodna_y(x, yn.get(iter + 1))) >= epsilon || Math.abs(yn.get(iter+1) - yn.get(iter)) >= epsilon) {
                yn.add(yn.get(iter) - (pochodna_y(x, yn.get(iter)) / pochodna_y2(x, yn.get(iter))));
                System.out.println("yn1 = " + yn.get(iter));
                iter++;
            }
        }
        if(xy == "x") return xn.get(iter);
        else return yn.get(iter);
    }

    public static void main(String[] args) {
        double x = 10, y = 10;
        double EPSILON = 0.001;
        double epsilon = 0.000001;
        int iter = 1;

        while(Math.abs(pochodna_xy(x,y)) > EPSILON) {

            System.out.println("x=" + x);
            x = metoda_stycznych(y, "x", epsilon);

            System.out.println("x=" + x);
            y = metoda_stycznych(x, "y", epsilon);

            System.out.println(x + " | " + y);

        }
        System.out.println(x + " | " + y);
    }