Originally Posted by

**NathanBUK** Hi, well got my exam tomorrow and this is the only topic area I struggle with soo much, a past paper i'm trying here asks this qustion:

It is given that $\displaystyle Sn=\sum(3r^2-3r+1)$

Use the formulae for $\displaystyle \sum(r^2)$ and $\displaystyle \sum(r)$ to show that $\displaystyle Sn=n^3$.

I know that I treat the +1 as n but I really dont know where I should take out factors or when I should expand etc. Also I get the formulas for the r squared and r so im aware of what they are.

Each time Ive tried Ive managed to get to either $\displaystyle n^3-1$ or $\displaystyle n(n^2+1)$

I would be really greatful if someone could explain what process I should do to get the answer.

Thankyou !