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Unformatted text preview: ejm753 – Review 3 (For Exam 3) – Cepparo – (58400) 1 This printout should have 23 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Determine whether the sequence { a n } con verges or diverges when a n = ( − 1) n parenleftbigg 4 n + 7 8 n + 8 parenrightbigg , and if it does, find its limit. 1. limit = 0 2. sequence diverges correct 3. limit = 1 2 4. limit = 7 8 5. limit = ± 1 2 Explanation: After division, 4 n + 7 8 n + 8 = 4 + 7 n 8 + 8 n . Now 7 n , 8 n → 0 as n → ∞ , so lim n →∞ 4 n + 7 8 n + 8 = 1 2 negationslash = 0 . Thus as n → ∞ , the values of a n oscillate be tween values ever closer to ± 1 2 . Consequently, the sequence diverges . 002 10.0 points Determine whether the series 3 + 2 + 4 3 + 8 9 + ··· is convergent or divergent, and if convergent, find its sum. 1. convergent with sum = 9 correct 2. convergent with sum = 1 4 3. divergent 4. convergent with sum = 4 5. convergent with sum = 1 9 Explanation: The series 3 + 2 + 4 3 + 8 9 + ··· = ∞ summationdisplay n =1 a r n − 1 is an infinite geometric series in which a = 3 and r = 2 3 . But such a series is (i) convergent with sum a 1 − r when  r  < 1, (ii) divergent when  r  ≥ 1 . Thus the given series is convergent with sum = 9 . 003 10.0 points Determine whether the infinite series ∞ summationdisplay n =1 3( n + 1) 2 n ( n + 2) converges or diverges, and if converges, find its sum. 1. converges with sum = 3 2 2. converges with sum = 3 8 3. diverges correct ejm753 – Review 3 (For Exam 3) – Cepparo – (58400) 2 4. converges with sum = 3 5. converges with sum = 3 4 Explanation: By the Divergence Test, an infinite series ∑ n a n diverges when lim n →∞ a n negationslash = 0 . Now, for the given series, a n = 3( n + 1) 2 n ( n + 2) = 3 n 2 + 6 n + 3 n 2 + 2 n . But then, lim n →∞ a n = 3 negationslash = 0 . Consequently, the Divergence Test says that the given series diverges . keywords: infinite series, Divergence Test, ra tional function 004 10.0 points To apply the root test to an infinite series ∑ n a n the value of ρ = lim n →∞  a n  1 /n has to be determined. Compute the value of ρ for the series ∞ summationdisplay n = 1 parenleftbigg 2 n + 6 3 n parenrightbigg 2 n . 1. ρ = 4 2. ρ = 2 3 3. ρ = 4 9 correct 4. ρ = 9 5. ρ = 2 Explanation: After division, 2 n + 6 3 n = 2 + 6 /n 3 , so  a n  1 /n = parenleftBig 2 + 6 /n 3 parenrightBig 2 . On the other hand, lim n →∞ 2 + 6 /n 3 = 2 3 . Consequently, ρ = 4 9 . keywords: /* If you use any of these, fix the comment symbols. 005 10.0 points Determine whether the series ∞ summationdisplay k = 1 ( − 1) k − 1 cos parenleftBig 1 2 k parenrightBig is absolutely convergent, conditionally con vergent or divergent....
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This note was uploaded on 04/28/2008 for the course M 408 L taught by Professor Cepparo during the Spring '08 term at University of Texas.
 Spring '08
 Cepparo

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