dok = 10^(-12);
f = @(x) sin(x);
df = @(x,h) (f(x+h) - f(x-k))/(2*h);
d2f = @(x,h) (f(x+h)-2*f(x)+f(x-h))/(h^2);
a = 1;
b = 4;
fa = f(a);
fb = f(b);
x1 = a;
x0 = b;

i = 0;

if (fa*fb <= 0)
    i = 0;
    while abs(x1 - x0) > dok

        i = i + 1;

        x1 = x0;
        x0 = a - fa * (b - a)/(fb - fa);
        f0 = f(x0);
        if abs(f0) < dok
            disp('Koniec');
            x1
            i
            break;
        end

        if fa*f0 < 0
            b = x0;
            fb = f0;
        else
            a = x0;
            fa = f0;
        end
    end
else
    disp('Funkcja nie spelnia warunkow');
end