1. ## Geometric sequences

I'm really troubled with this question. Can anybody help?
"If we have a geometric sequence with initial term a and ratio r, then is the formula for the ninth term of the corresponding geometric series is given by
s_n = a 1-r/1-r^n ?"

2. Originally Posted by 14041471
I'm really troubled with this question. Can anybody help?
"If we have a geometric sequence with initial term a and ratio r, then is the formula for the ninth term of the corresponding geometric series is given by
s_n = a 1-r/1-r^n ?"
The geometric sequence formula is $S_n= a\frac{1-r^n}{1-r}$.

You should have a constant value of the initial term and the ratio thus to find the ninth term, you will set $n=9$.