An arithmetic sequence has first term 5 and common difference 9. Find term 28.
Answer and explanation
248
5 + (28 − 1) × 9 = 248
Subjects
Sequences & series
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Sample exercises
Find the sum of the first 20 terms of an arithmetic sequence with first term 18 and common difference 2.
Answer and explanation
740
20 × (2 × 18 + (20 − 1) × 2) ÷ 2 = 740
A geometric sequence starts at 3, with common ratio 5. Find term 6.
Answer and explanation
9375
3 × 5^(6 − 1) = 9375
Study notes
Arithmetic sequences
The first term is n = 1. Use one fewer step than the term number.
Grades 9–12Sum of an arithmetic sequence
Pair the first and last terms; each pair has the same total.
Grades 10–12Geometric sequences
Multiply repeatedly by the common ratio; do not add it.
Grades 10–12Finite geometric sums
Use n terms, starting with the first term a.
Grades 10–12Sequences & series · Formula sheet
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Grades 9–10Sequences & series · Formula sheet
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