Hi, sorry can't seem to figure this out..please help me ..?
1+3=4
1+3+9=13
1+3+9 +27 = 40
and so on..
find an expression for this sequence
any guidance would help soo much .. so lost!!
Those are powers of three so this is a geometric series. The sum of the geometric series $\displaystyle \sum_{i= 0}^n ar^{n}= a\frac{r^{n+1}- 1}{r- 1}$. Here, a= 1, r= 3.