Geometric series

What is a Geometric Progression?

In this video you are shown what a geometric progression is, the formulae used along with an example.

Example on finding the 1st term, common ratio and sum

This is a typical example where you are given terms in a geometric progression and asked to find the first term, common ratio and the sum of a certain number of terms.

  1. If the 6th term of a geometric series is 972 and the 9th term is 26244.
    Find the 1st term, the common ratio and the sum of the first 10 terms.

Example on Consecutive Terms

Questions involving consecutive terms can be easily worked out if you set up a ratio equation between the terms as the video shows.

  1. If 2x + 5, 6x – 10 and 8x + 20 are consecutive terms in a geometric series. Find the possible values of x and the corresponding terms.

Example on Investing

In this example I show you how the geometric progression can be used in an investment style problem. These problems can be quite tricky but worth learning.

  1. A girl invests £500 at the start of each year in an account paying 3.5% interest per year. At the start of each year he puts in another £500. After how many years has his account accumulated more than £20,000?

New · Axi

Stuck on this topic?

Axi, our AI tutor, answers questions on Geometric series – no copying, no pasting, no sign-up.