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A recursive sequence defines each term using previous terms. The Fibonacci sequence is the most famous example (each term is the sum of the two before it). Many real-world processes follow recursive patterns.
Công thức
General form: aₙ = f(aₙ₋₁, aₙ₋₂, ...) with initial conditions
- aₙ
- nth term of sequence
- aₙ₋₁, aₙ₋₂,...
- previous terms
- f
- recurrence relation function
Hướng dẫn từng bước
- 1Define base cases: a₀, a₁
- 2Define recurrence: aₙ = f(aₙ₋₁, aₙ₋₂)
- 3For aₙ = p×aₙ₋₁ + q×aₙ₋₂
- 4Fibonacci is p=1, q=1
Ví dụ có lời giải
đầu vào
a₀=1, a₁=1, aₙ=aₙ₋₁+aₙ₋₂
Kết quả
1,1,2,3,5,8,13,21 (Fibonacci)
đầu vào
a₀=1, a₁=2, aₙ=2aₙ₋₁−aₙ₋₂
Kết quả
1,2,3,4,5,6 (arithmetic)
Câu hỏi thường gặp
What is the difference between a recursive and explicit formula?
Recursive: defines aₙ using prior terms. Explicit: gives aₙ directly in terms of n.
Can every recursive sequence be expressed as explicit?
Not always easily. Some recursive sequences are difficult to express in closed form.
What are initial conditions in a recursive definition?
The first few terms (e.g., a₀ or a₁, a₂) that anchor the recursion so you can compute all later terms.
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