The impact of a drug is a measure of its effect, for example, the reduction in blood pressure, loss of weight, or the duration of a headache. The impact, I, generally depends on the dose, D, given. For positive constants a and b, two possible impact functions, valid for 0 ≤ D ≤ 300, are I = f(D) = aD√b + D  I = g(D) = aD√b − D.

(a) Which function, f or g, has a critical point for D > 0?
(b) For f and g and a = 1 and b = 300, what dose gives the maximum impact on 0 ≤ D ≤ 300?