Show that if a 0 and b2 ac 0, then 1 confidence interval on x0 is b b2

Show that if a ≥ 0 and b2 − ac ≥ 0, then 1 − α confidence interval on x0 is −b − √b2 − ac a ≤ x0 ≤ −b + √b2 − ac a .