Finding f(x) for a Riemann Sum - having trouble factoring out 'n'.

Question

SE,

I've been given this problem to evaluate: [the problem][1]

And here's my attempt at a solution: I'm getting stuck at creating f(x)

I've added the step numbers for reference, and hope to be given a push in the right direction.

Thank you.

Answer 1

Hint:

\begin{align} \frac{i}{n^2+i^2} = \frac{i}{1+(i/n)^2}\frac{1}{n^2}= \frac{(i/n)}{1+(i/n)^2}\frac{1}{n}. \end{align}