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Geometric Sequences Flashcards
GCSE Mathematics (Edexcel) 1MA1
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Geometric sequence
A sequence where each term is found by multiplying the previous term by a constant value called the common ratio.
Common ratio
The constant value by which each term in a geometric sequence is multiplied to get the next term.
Finding the common ratio
Divide any term in the sequence by the previous term.
General term of a geometric sequence
The nth term of a geometric sequence is given by the formula a × r^(n-1), where a is the first term and r is the common ratio.
First term (a)
The first term in a geometric sequence, represented by 'a' in the nth term formula.
nth term formula for geometric sequence
a × r^(n-1), where a is the first term, r is the common ratio, and n is the term number.
Example of a geometric sequence
2, 6, 18, 54... (common ratio is 3).
Identifying a geometric sequence
Check if the ratio between consecutive terms is constant.
Sum of a finite geometric sequence
The sum of the first n terms is given by the formula S_n = a(1 - r^n) / (1 - r), where r ≠ 1.
Sum of an infinite geometric sequence
If |r| < 1, the sum to infinity is S = a / (1 - r).

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