Hello, if someone could please help me with this problem, I'd really appreciate it. Here's a screenshot, to save the complicated typing:
Here $\displaystyle \Delta x = \frac{2}{n}$
and $\displaystyle x_i = \frac{2i}{n}$ so each $\displaystyle x_i$ increases by $\displaystyle \Delta x$ as i increases by 1.
So $\displaystyle R_n = \Sigma_{i=1}^n f(\frac{2i}{n})\frac{2}{n}
=\frac{2}{n} \Sigma_{i=1}^n [(\frac{2i}{n})^2 /2 - 8]$
Is that enough of a start?