1) The maximum possible value for f(2) under the question is 2 + 6*2 = 2 + 12 = 14. 2) can f(5) be negative ? ANSWER. YES. Take, for example, f(x) = 2 - x. Then f(0) = 2 and f(5) = 2 - 5 = -3, and f(x) satisfies all imposed conditions. can f(5) be equal to 0 ? ANSWER. YES. Take, for example, f(x) = 2 - 0.4x.