function parabola2( a, b, c)
%PARABOLA Summary of this function goes here
%   Detailed explanation goes here

    rts = sort(roots([a b c]));
    
    if isreal(rts)
        x1 = rts(1);
        x2 = rts(2);  
        d = (x2 - x1)/2;
    else
        x1 = -b / (2*a);
        x2 = x1;
        d  = abs(c);
    end

    if x1 == x2
        d = max([abs(d) 2*d 10]);
    end
    
    x = x1-d:.1:x2+d;
    y = a*x.^2 + b*x + c;
    plot(x, y);
end