f x x x 18x 4 Over which of these domains could you define f x Remember that f x must be one to one only one y value for each x value over the domain where f x is defined as a function So in some cases you must restrict the domain of f x so that it s one to one There might be more than one section of domain that s one to one HINT The function f x is one to one wherever it s monotonic monotonic simply means increasing or decreasing over the entire interval so the derivative does not change sign To find these intervals start by taking the first derivative which is f x 3x 3x 18 and setting it equal to zero 1 3 II 3 III 2 00 OA Either I or II B Either I or III C II OD I E III