1. ## Series/Sequences

If Sn = n^2 + 3n, determine an expression for tn.

How do I find tn?

I know my formulas for finding the sum, but I don't know how to find tn.

Do I use the formulas for arithmetic or geometric? Thanks for some guidance.

2. $T_{n}=S_{n}-S_{n-1}=[n^{2}+3n]-[(n-1)^{2}+3(n-1)]=...$

Can you continue?