Consider the cubic polynomial f(x)=x3−3kx2+9x+5, where k∈R.
(i) Find f′(x).
(ii) Determine the condition on k that makes f′(x) positive for every real x.
(iii) Using the result obtained in (ii), find the set of real values of k for which the function f is strictly increasing on (−∞,∞).