Q) The function f is defined by f : x → 2x^2 − 12x + 13 for 0 ≤ x ≤ A, where A is a constant

(i) Express f(x) in the form a(x + b)2 + c, where a, b and c are constants.

(ii) State the value of A for which the graph of y = f(x) has a line of symmetry

(iii) When A has this value, find the range of f

My Attempt

$\displaystyle 2x^2-12x+13$

$\displaystyle 2(x-3)^2-5$

Now I have no clue on how to do (ii) which is linked with (iii). Will appreciated your help!

Thanks!