# Week 2 – Geometric Sequences

This week in pre-calculus 11, we learned geometric sequences and geometric series. I learned how to find $S_n$ with just the first term and r. I did find it a little complicated but when I used the formula $S_n=\frac{a(r{^n}-1)}{r-1}$ I could figure it out and it made sense.

For example (Page 49, #5a, Pre-calculus worktext):

$S_n=\frac{a(r{^n}-1)}{r-1}$

$S_8=\frac{1(0.3{^7}-1)}{0.3-1}$

$S_8=\frac{-0.99}{-0.7}$

$S_n=1.41$