Series, pls help!!

Below are my answers:


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3 s_n = 2 - 0.8^n. Let n -> ∞, Σ (1->∞) a_n = 216(a) and (b) no difference as i and j are dummy index17 As ratio -4/3 > 1, the geometric series is divergent18 S = a/(1 - r) = 1/8/(1 + 1/2) = 1/1219 S = a/(1 - r) = 10/(1 + 1/5) = 50/635 As (n^2 + 1)/(2n^2 + 1) -> 0 and ln 0 = -∞. The series is divergent39 Consider a_n = arctan nThen a_n = π/2 (n -> ∞), So the series is divergent