If the quadratic functions F1 (x) = a1x2 + b1x + C1 and F2 (x) = a2x2 + b2x + C2, let F1 (x) + F2 (x) be an increasing function on (- ∞, + ∞) if______ .

If the quadratic functions F1 (x) = a1x2 + b1x + C1 and F2 (x) = a2x2 + b2x + C2, let F1 (x) + F2 (x) be an increasing function on (- ∞, + ∞) if______ .

From the meaning of the question, we can get that F1 (x) + F2 (x) can be a linear function, and the coefficient of the linear term is a positive real number, a1 + A2 = 0 and B1 + B2 > 0; so the answer is: a1 + A2 = 0 and B1 + B2 > 0