function [ x,fx,n ] = KubniMetod( fun,fund,x1,x2,tol )
%KUBNIMETOD Summary of this function goes here
%   Detailed explanation goes here
n = 1;
X = [x1 x2]';
F = feval(fun,X);
dF = feval(fund, X);
f = [F(1);F(2);dF(1);dF(2)];
Y = [1 X(1) X(1)^2 X(1)^3;1 X(2) X(2)^2 X(2)^3; 0 1 2*X(1) 3*X(1)^2; 0 1 2*X(2) 3*X(2)^2];
abcd = Y \ f;
b = abcd(2);
c = abcd(3);
d = abcd(4);

% -b +- sq(b^2 - 4ac) / 2a;
xa = (-2*c + sqrt((2*c)^2 - 4 * b * 3*d)) / (2 * b);
xb = (-2*c - sqrt((2*c)^2 - 4 * b * 3*d)) / (2 * b);
if ~(xa > x1 && xa<x2)
    x = xb;
elseif ~(xb > x1 && xb < x2)
    x = xa;
else
    if xa < xb
        x = xa;
    else
        x = xb;
    end
end
while abs([1 x x^2 x^3]*abcd - feval(fun,x))>tol
    n = n + 1;
    if feval(fund,x) < 0
        x1 = x;
    else
        x2 = x;
    end
    X = [x1 x2]';
    F = feval(fun,X);
    dF = feval(fund, X);
    f = [F(1);F(2);dF(1);dF(2)];
    Y = [1 X(1) X(1)^2 X(1)^3;1 X(2) X(2)^2 X(2)^3; 0 1 2*X(1) 3*X(1)^2; 0 1 2*X(2) 3*X(2)^2];
    abcd = Y \ f;
    b = abcd(2);
    c = abcd(3);
    d = abcd(4);
    xa = (-2*c + sqrt(c^2 - 4 * b * 3* d)) / 2 * b;
    xb = (-2*c - sqrt(c^2 - 4 * b * 3 * d)) / 2 * b;
    if ~(xa > x1 && xa<x2)
        x = xb;
    elseif ~(xb > x1 && xb < x2)
        x = xa;
    else
        if xa < xb
            x = xa;
        else
            x = xb;
        end
    end

end
fx = feval(fun,x);
end