Misc 12 - Chapter 8 Class 11 Sequences and Series

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Misc 12 Find the 20th term of the series 2 × 4 + 4 × 6 + 6 × 8 + … + n terms. Now, an = [nth term of 2, 4, 6 …] × [nth term of 4, 6, 8 …] = (2n) (2n + 2) = (2n) (2(n + 1)) = 4n (n + 1) Thus, nth term of series 2 × 4 + 4 × 6 + 6 × 8… is an = 4n (n + 1) We need to find 20th term of given series Putting n = 20 a20 = 4 × 2(20 + 1) = 80 (21) = 1680 Hence 20th term of series is 1680

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Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science and Computer Science at Teachoo