Question

The 8th term of an arithmetic sequence is 3 and the 100th term is 49. What is the recursive formula for the sequence?

Answer 1

uₙ₊₁ = uₙ + ¹/₂

Explanation:

uₙ₊₁ = uₙ + d

u₈ = 3

u₁₀₀ = 49

We can establish the following:

u₉ = 3 + d

u₁₀ = (3 + d) + d = 3 + 2d

u₁₁ = (3 + 2d) + d = 3 + 3d

so...

u₈₊ₐ = 3 + ad

u₁₀₀ = u₈₊₉₂ = 3 + 92d

3 + 92d = 49

92d = 46

d = ¹/₂

∴ uₙ₊₁ = uₙ + ¹/₂