Geometric sequences and seriesEdexcel International A Level Maths: Flashcards

What these 12 flashcards ask

nth term of a geometric sequence?
Sum of the first n terms of a geometric series?
Sum to infinity?
Condition for a sum to infinity to exist?
How do you find r from two terms?
S\infty-Sn in terms of a, r, n?
a=6, r=\frac12. Find S\infty.
When do you use logs with a geometric series?
When must you reverse an inequality using logs?
Proof of Sn: first step?
ar=12, S\infty=64. Equation in r?
What is a geometric sequence?

Exam questions on Geometric sequences and series

A geometric series has first term $6$ and common ratio $\frac12$ .
Find the exact sum of the first $8$ terms.2 marks
A geometric series has first term $5$ and common ratio $1.2$ . Its $n$ th term is $u_n$ .
Find the sum of the first $15$ terms, giving your answer to 3 significant figures.2 marks
A geometric series with positive common ratio has second term $24$ and fourth term $6$ . The sum of the first $n$ terms is $S_n$ .
Find the first term and the common ratio.3 marks

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).