9 [Maximum mark: 13] Let f(x)=x+6x+(8+k). a Find the discriminant, D, of this quadratic, in terms of k. [2 marks] b Given that f(x) > 0 for all values of x, state, with reasons, the set of values that can be taken by i Diik. [5 marks] c Write f(x) in the form f(x) = (x+p)+q, where pe Z and q is an expression involving k d Explain how the form obtained in c confirms the answer to b ii. e If k = 4, write down the minimum point of the quadratic. [2 marks] [2 marks] [2 marks]