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Unformatted text preview: Math 20D  Spring 2006  Midterm 2 Prof. Mike Zabrocki score 1 24 2 25 3 25 4 26 BONUS 10 total 100 Name: Time of section: 1. Determine if the following sums diverge, converge absolutely or converge conditionally. State which test you use to justify your answer and the conclusion which follows from that test. (a) n =1 (1 cos(1 /n )) (b) n =2 ( 1) n n 2 n 1 cos(1 /n ) = 1 1 + (1 /n ) 2 2! (1 /n ) 4 4! + This is an alternating series and 1 2 n n Therefore, lim n 1 cos(1 /n ) 1 /n 2 = 1 / 2 is positive and decreasing and lim n 1 2 n n = 0 since 1 n 2 converges then by L.C.T. Hence by A.S.T. converges conditionally. then n =1 (1 cos(1 /n )) converges Since lim n 1 2 n n 1 / 2 n = 1 then by L.C.T. absolutely. n =2 ( 1) n n 2 n converges absolutely since 1 / 2 n converges. (c) n =1 cos( n ) 1 cos( n ) (d) n =1 1 n (1 e 1 /n ) The series is alternating but 1 n (1 e 1 /n ) = 1 n (1 1 1 n ( 1 n ) 2 2! ) lim n 1 1 cos ( n ) 6 = 0 lim n 1 n (1 e 1 /n ) 1 n 3 / 2 = 1 so the series diverges by divergence test therefore n =1 1 n (1 e 1 /n ) converges absolutely since...
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 Spring '06
 Mohanty
 Math

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