function xrez = kubnaMetoda( f, fprim, j, k, greska)
%UNTITLED Summary of this function goes here
%   Detailed explanation goes here


syms a b c d

x0 = j;
x1 = k;

eqn1 = a + b*x0 + c*(x0^2) + d*(x0^3) == feval(f, x0);
eqn2 = a + b*x1 + c*(x1^2) + d*(x1^3) == feval(f, x1);
eqn3 = b + c*x0 + d*(x0^2) == feval(fprim, x0);
eqn4 = b + c*x1 + d*(x1^2) == feval(fprim, x1);

[a, b, c, d] = solve(eqn1, eqn2, eqn3, eqn4);

g = @(x) a + b*x + c*(x^2) + d*(x^3);
gprim = @(x) b + c*x + d*(x^2);

xzvezd1 = (-c + sqrt(4*b*d-c^2))/(2*b);
xzvezd2 = (-c - sqrt(4*b*d-c^2))/(2*b);

%ako bude pravio problem
%stavi xzvezd1 = double(xzvezd1) mada ne bi trebao da bude problem sa
%racionalnim brojevima
%xzvezd1 = 1;
%xzvezd2 = 1.5;

if((xzvezd1 > 2) || (xzvezd1 < 0))
    x = xzvezd2;
elseif((xzvezd2 > 2) || (xzvezd2 < 0))
    x = xzvezd1;
else
    if(feval(f, xzvezd1) > feval(f, xzvezd2))
        x = xzvezd2;
    else
        x = xzvezd1;
    end
end

if(feval(fprim, x) > 0)
    x1 = x;
elseif(feval(xprim, x) < 0)
    x0 = x;
else
    %ne znam, valjda je to onda to
end

while (abs(feval(f, x) - feval(g, x)) > greska)

    eqn1 = a + b*x0 + c*(x0^2) + d*(x0^3) == feval(f, x0);
    eqn2 = a + b*x1 + c*(x1^2) + d*(x1^3) == feval(f, x1);
    eqn3 = b + c*x0 + d*(x0^2) == feval(fprim, x0);
    eqn4 = b + c*x1 + d*(x1^2) == feval(fprim, x1);

    syms a b c d

    [a, b, c, d] = solve(eqn1, eqn2, eqn3, eqn4);

    g = @(x) a + b*x + c*(x^2) + d*(x^3);
    gprim = @(x) b + c*x + d*(x^2);


    xzvezd1 = (-c + sqrt(4*b*d-c^2))/(2*b);
    xzvezd2 = (-c - sqrt(4*b*d-c^2))/(2*b);

    %isto resenje ako bude problem kao i gore

    if((xzvezd1 > 2) || (xzvezd1 < 0))
        x = xzvezd2;
    elseif((xzvezd2 > 2) || (xzvezd2 < 0))
        x = xzvezd1;
    else
        if(feval(f, xzvezd1) > feval(f, xzvezd2))
            x = xzvezd2;
        else
            x = xzvezd1;
        end
    end

    if(feval(fprim, x) > 0)
        x1 = x;
    elseif(feval(xprim, x) < 0)
        x0 = x;
    else
        %ne znam, valjda je to onda to
    end

end

xrez = x;

end

kubnaMetoda(@(x) 2*x^4-3*x, @(x) 8*x^3-3, 0.5, 2, 10^-5)