OCR A-level Maths Geometric sequences
This page covers the following topics:
1. Basics of geometric sequences
2. Terms in a geometric sequence
3. nth term of geometric sequences
4. Geometric series
5. Convergent sequences
In a geometric sequence, all terms are multiplied or divided by the same value. For example, the sequence 2, 4, 8, 16, ... is geometric, as each term is twice the previous term.
The term to term rule in a geometric sequence is multiplying or dividing by the same value, also known as the common ratio (r). The common ratio is determined by dividing one term by the previous term.
The nth term, or general term, of a geometric sequence is given by a formula (see image).
A geometric sequence (i.e. a list of terms) can also be represented as a geometric series (a sum of terms). Sigma notation (see image) is used to calculate the sum of a finite number of terms of a geometric sequence.
An infinite series has an infinite number of terms. The partial sum (Sₙ) of these terms is the sum of the first n terms. If Sₙ approaches a finite limit (known as the sum to infinity), the series is convergent. In a geometric series, if |r|< 1, the sum to infinity can be calculated with a formula (see image).
Is the sequence 1, 2.7, 8, −15, ... geometric?
What is the 5th term of the geometric sequence 1.2, 0.168, 0.02352, ...?
Calculate the next three terms of the geometric sequence 11, 7.7, 5.39, ....
Is the sequence 6, 3, 1.5, ... geometric? Explain your answer.
If |r| > 1, a geometric series is convergent. True or false? Explain your answer.
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