Quadratic Breakdown....

(* This is the way we learned it in school: *)
quadraticRoots[a_,b_,c_]:={(-b+Sqrt[b^2-4a*c])/(2*a),(-b-Sqrt[b^2-4a*c])/(2*a)}
quadraticRoots[.2,-7,.001]

(* This form is good if b<0 *)
quadraticRoots[a_,b_,c_]:={(-b+Sqrt[b^2-4a*c])/(2*a),2*c/(-b+Sqrt[b^2-4a*c])}
quadraticRoots[.2,-7,.001]

(* This form is good if b>0 *)
quadraticRoots[a_,b_,c_]:={2*c/(-b-Sqrt[b^2-4a*c]),(-b-Sqrt[b^2-4a*c])/(2*a)}
quadraticRoots[.2,-7,.001]

So here’s a form that gets it “right” in general:

quadraticRoots[a_,b_,c_]:=
If [b>0,
{2*c/(-b-Sqrt[b^2-4a*c]),(-b-Sqrt[b^2-4a*c])/(2*a)},
{(-b+Sqrt[b^2-4a*c])/(2*a),2*c/(-b+Sqrt[b^2-4a*c])}]
quadraticRoots[.2,-7,.001]