$$f(x) = \left(1 + \frac{x}{k}\right)^n, \quad k, n \in \mathbb{N}, \quad n > 2.$$
Given that the coefficient of \(x^3\) is twice the coefficient of \(x^2\) in the binomial expansion of \(f(x)\),
- prove that \(n = 6k + 2\). [3]
Given also that the coefficients of \(x^4\) and \(x^5\) are equal and non-zero,
- form another equation in \(n\) and \(k\) and hence show that \(k = 2\) and \(n = 14\). [4]
Using these values of \(k\) and \(n\),
- expand \(f(x)\) in ascending powers of \(x\), up to and including the term in \(x^5\). Give each coefficient as an exact fraction in its lowest terms [4]