(1) Find arithmetic sequence 8, 5, 2 (2) judge whether - 401 is an arithmetic sequence - 5, - 9, - 13 What's your item? If yes, which item is it? If not, explain the reason
(1) Arithmetic sequence 8, 5, 2 Among them, A1 = 8, d = 5-8 = - 3, n = 20 ∥ an = a1 + (n-1) d = - 3N + 11 ∥ A20 = 11-3 × 20 = - 49 (4 points) (2) arithmetic sequence - 5, - 9, - 13 Where, A1 = - 5, d = - 9 - (- 5) = - 4 ∧ an = - 5 + (n-1) × (- 4) = - 4N-1, let - 401 = - 4N-1, then & nbsp; n = 100 ∧ - 401 is the 100th term of the sequence (8 points)
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