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Unformatted text preview: MAT 127, Lecture 01, Spring 2011 Solutions to Midterm 1 Test the following series for convergence. 1. ∑ ∞ n =1 ne n . Answer: Divergent. Solution: Let us use the Ratio Test: a n = ne n , a n +1 = ( n + 1) e n +1 , L = lim n →∞ a n +1 a n = lim n →∞ ( n + 1) e n +1 ne n = e · lim n →∞ n + 1 n = e. Since L > 1, the series is divergent. 2. ∑ ∞ n =1 3+( 2) n 5 n . Answer: Convergent. Solution: Remark that 3 + ( 2) n 5 n = 3 5 n + ( 2) n 5 n . The first series is a geometric series with a 1 = 3 5 and r 1 = 1 5 . The second series is a geometric series with a 2 = 2 5 and r 2 = 2 5 . Since  r 1  < 1 ,  r 2  < 1, both series are convergent, and their sum is convergent too. 3. ∑ ∞ n =1 ( n !) n (2 n )! . Answer: Convergent. Solution: Let us use the Ratio Test: a n = ( n !) n (2 n )! , a n +1 = (( n + 1)!)( n + 1) (2 n + 2)! , 1 L = lim n →∞ a n +1 a n = lim n →∞ ( n + 1)! · ( n + 1) · (2 n )!...
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This note was uploaded on 01/25/2012 for the course MAT 127 taught by Professor Guanyushi during the Fall '07 term at SUNY Stony Brook.
 Fall '07
 GuanYuShi
 Calculus

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